Evaluation of traditional grain store buildings (hórreos) in Galicia (NW Spain): Analysis of outdoor/indoor temperature and humidity relationships

Abstract

Hórreos are traditional rural buildings of northern Spain used for desiccation and conservation of cereal grains. They provide natural ventilation, an unfavourable environment to discourage attack by biotic agents (e.g., fungi and insects) and prevent access by others, such as rodents. The objective of this paper was to study the environmental conditions of the Mondoñedo type of hórreos (north coastal area of Galicia, northwestern Spain). They are built of wood and stone, with a prismatic grain chamber isolated from the ground and with ventilation openings on the side walls. In three hórreos, over a period of one month, the temperature (T) and relative humidity (RH) of the indoor and outdoor air were measured throughout the day. Maximum and minimum values during three periods (night, morning and afternoon) and at three specific times (9:00, 14:00 and 21:00) were analysed. It was noted that hórreos had a dampening effect on RH. When the outdoor humidity was ≥ 90%, the indoor humidity was on average 5.2% lower. If the outdoor humidity was ≤ 65%, the indoor humidity was on average 3.2% higher. When it was around 75%, this effect was at its smallest. This effect was not as remarkable for T. It is concluded that RH and, to a lesser extent, T remain more stable in the hórreo than outdoors, providing an appropriate environment for the preservation of grain. Other characteristics (i.e., geographical location, topographic altitude, exposure to the wind and longitudinal axis direction) appear to influence the amount of change experienced by these parameters.

Full text

Evaluation of traditional grain store buildings (hórreos)
in Galicia (NW Spain): analysis of outdoor/indoor temperature
and humidity relationships
O. A. Perez-Garcia1, X. C. Carreira1, E. Carral2*, M. E. Fernandez1and R. A. Mariño1
1 Department of Agroforestry Engineering. University of Santiago de Compostela. Escola Politécnica Superior.
Campus Universitario. 27002 Lugo. Spain
2 Department of Cellular Biology and Ecology/IBADER (Institure for Rural Development and Biodiversity).
University of Santiago de Compostela. Escola Politécnica Superior. Campus Universitario. 27002 Lugo. Spain
Abstract
Hórreos are traditional rural buildings of northern Spain used for desiccation and conservation of cereal grains.
They provide natural ventilation, an unfavourable environment to discourage attack by biotic agents (e.g., fungi and
insects) and prevent access by others, such as rodents. The objective of this paper was to study the environmental
conditions of the Mondoñedo type of hórreos (north coastal area of Galicia, northwestern Spain). They are built of
wood and stone, with a prismatic grain chamber isolated from the ground and with ventilation openings on the side
walls. In three hórreos, over a period of one month, the temperature (T) and relative humidity (RH) of the indoor and
outdoor air were measured throughout the day. Maximum and minimum values during three periods (night, morning
and afternoon) and at three specific times (9:00, 14:00 and 21:00) were analysed. It was noted that hórreos had a
dampening effect on RH. When the outdoor humidity was ≥90%, the indoor humidity was on average 5.2% lower. If
the outdoor humidity was ≤65%, the indoor humidity was on average 3.2% higher. When it was around 75%, this
effect was at its smallest. This effect was not as remarkable for T. It is concluded that RH and, to a lesser extent, T
remain more stable in the hórreo than outdoors, providing an appropriate environment for the preservation of grain.
Other characteristics (i.e., geographical location, topographic altitude, exposure to the wind and longitudinal axis
direction) appear to influence the amount of change experienced by these parameters.
Additional key words: ambient parameters analysis; cereal grain conservation; rural traditional buildings.
Resumen
Evaluación de construcciones tradicionales para el almacenamiento de granos (hórreos) en Galicia
(NO de España): análisis de las relaciones entre la temperatura y humedad interior y exterior
Los hórreos son construcciones rurales tradicionales del norte de España usadas para la desecación y conservación
de granos de cereal. Sus características proporcionan ventilación natural y un ambiente desfavorable para el ataque
de agentes bióticos (como hongos o insectos), además de evitar el acceso de otros, como roedores. El objetivo de es-
te trabajo fue estudiar las condiciones ambientales de los hórreos tipo Mondoñedo (zona costera norte de Galicia, nor-
oeste de España). Están construidos de madera y piedra, con una cámara de grano prismática aislada del suelo y con
aberturas de ventilación en sus paredes laterales. En tres hórreos, durante un periodo de un mes, se midieron la tem-
peratura y la humedad relativa del aire interior y exterior a lo largo del día. Se analizaron los valores máximos y mí-
nimos durante tres periodos (noche, mañana y tarde) y a tres horas determinadas (9:00, 14:00 y 21:00). Se observó
que los hórreos tenían un efecto amortiguador sobre la humedad relativa: Cuando la humedad exterior era ≥90% ó
≤65%, la humedad interior era, como media, un 5,2% inferior o un 3,2% superior, respectivamente; si era ~75% el
efecto era el más reducido. Para la temperatura, este efecto no era tan destacable. Se concluye que la humedad relati-
va y, en menor medida, la temperatura permanecen más estables dentro del hórreo, proporcionando un ambiente apro-
piado para preservar el grano. Otras características (como localización geográfica, altitud topográfica, exposición al
viento y dirección del eje longitudinal) parecen influir en el nivel de variación experimentado por las variables.
Palabras clave adicionales: análisis de parámetros ambientales; conservación de cereales; construcciones rurales
tradicionales.
* Corresponding author: emilio.carral@usc.es
Received: 07-04-09; Accepted: 21-07-10.
X. C. Carreira, M. E. Fernández and R. A. Mariño are members of the SEA.
Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) Spanish Journal of Agricultural Research 2010 8(4), 925-935
Available online at www.inia.es/sjar ISSN: 1695-971-X
eISSN: 2171-9292

Introduction
The grain store, or hórreo, typical of Galicia (north-
western Spain) is a rural building for storing grains of
cereal, mainly maize (Zea mays L.). There are about
thirty thousand of these buildings in this region. They
are of great importance from historical, anthropolo-
gical, economic, architectural and cultural points of
view. The word «hórreo» apparently has its origins in
granarium horreum, the name given by the Romans to
a special kind of grain store (De Llano, 1983). In the
early 17th century, the arrival of maize in Galicia from
the American continent marked the beginning of an
important specialisation of these buildings for the
preservation of this cereal.
The conservation of cereals in general and maize in
particular involves careful storage to prevent damage
by biotic and abiotic agents. White (1992) indicated
that grain bulks form distinct ecosystems in which the
grains and communities of insects, mites, microflora
and, occasionally, rodents and birds interact in a single
environment. Food availability and proper environmental
conditions will favour the growth of fungi and insects.
Therefore, the control of these agents is different from
that of rodents and birds, where one key is to limit
physical access.
The temperature and humidity can be considered as
fundamental abiotic agents; high values favour the ger-
mination of seeds and affect their quality characteris-
tics and also encourage the development of some biotic
agents (fungi, insects).
In the case of fungi, grains transport microflora and
storage fungi whose ability to germinate depends on
the availability of water in the substrate, temperature
and intragranular gas composition (Magan and Lacey,
1988; Gagiu et al., 2007). Monitoring the biophysical
conditions of storage is necessary for mould manage-
ment (Yigezu et al., 2008; Rozman et al., 2008).
Temperature management is also a biorational tool
to control insects (Phillips and Throne, 2010), although
the humidity and the presence of damaged grains also
influence the likelihood of insect attacks (Cox and
Collins, 2002).
Therefore, the Galician hórreo is more than just a
granary. It is also involved in desiccation of the grain
to guarantee its preservation, due to its geometric and
architectural characteristics. There are different sorts
of hórreos depending on the shape of the building, the
roof features, the supports, the kind of materials used
and the geographical location (De Llano, 1983; Martínez
Rodríguez, 1999). In the coastal areas near the Canta-
brian Sea (the Mariña Central area in the province of
Lugo) there are two types, Ribadeo and Mondoñedo.
Usually, the Mondoñedo hórreos preserve traditional
features in a better form. The fundamental difference
between them is the material used to construct the side
walls (wood in the Mondoñedo type and stone in the
Ribadeo type).
These hórreos are tall, narrow buildings with a rec-
tangular layout. They have raised floors that insulate
them from the ground and prevent access by rodents.
They also have numerous openings in the side walls to
permit natural ventilation and control the indoor rela-
tive humidity (RHi). In this way, the grain desiccation
is supported as well as the maintenance of an optimum
humidity level of the grain. The hórreos’ characteristics
meet current energy-efficient criteria, in this case with
null energy consumption, within the context in which
they were conceived. This is the case of traditional buil-
dings that are adapted to the environment (Chen et al.,
1997; Sozen and Gedik, 2007; Van Hoof and Van Dijken,
2008). Other traditional buildings may also be adapted
to the climatic characteristics of their geographic loca-
tion (Oktay, 2002).
The hypothesis considered in this paper regarding
hórreos was that their particular building features permit
natural ventilation and make particular indoor environ-
mental conditions possible; thereby, they offer adequate
conditions for storage of grains. In a broader sense,
they serve as an example of traditional buildings that
meet the present criteria of energy-efficient design of
buildings (i.e., with lower energy consumption during
use, in this case no energy consumption).
The aim of this paper was to study the indoor envi-
ronmental conditions of Galician hórreos. For this pur-
pose, the RH and air T were measured outside and
inside of three hórreos of the same type (Mondoñedo)
located in different geographic locations (coastal or
mountain area) in municipalities adjacent to the Can-
tabrian Sea in the Galician province of Lugo.
The comparative analysis between indoor and out-
door parameters at different times of the day had three
926 O. A. Pérez-García et al. / Span J Agric Res (2010) 8(4), 925-935
Abbreviations used: RH (relative humidity), T (temperature), RHi (indoor relative humidity), RHo (outdoor relative humidity),
Ti (indoor temperature), To (outdoor temperature), RHmax (maximum relative humidity), RHmin (minimum relative humidity),
Tmax (maximum temperature), Tmin (minimum temperature).

goals: i) to estimate whether the natural regulation of
the environment by the constructive characteristics of
the hórreo led to significant differences between the
characteristics of the indoor and outdoor air; ii) to
define the relationships that permit estimating the
indoor foreseeable RH and T based on external values;
and iii) to investigate whether any factor can explain
most of the variation in environmental parameters of
the hórreos with respect to the outside air characteristics.
Material and methods
Building description
The Galician hórreos have two basic design features.
The first is the separation of the body of the building
from the ground. It is a room, a grain chamber with a
floor raised on support elements. The second is the nu-
merous openings in the walls to encourage ventilation.
The structure and the walls can be constructed of wood
or stone. The covering material can be slate or tile. All
of these features are used as classification criteria (De
Llano, 1983; Martínez-Rodríguez, 1999).
The grain chamber is insulated from the ground
using bases or support elements (called «feet», «pies»
in Spanish, or «pes» in the Galician language). These
elements permit the isolation of the chamber from soil
moisture while placing it at a greater height to facilitate
ventilation and to prevent access by rodents. The bases
can be either individual supports or continuous masonry
prisms. There are also elements made of stone between
the bases and the grain chamber that are used to prevent
rodents from climbing the supports.
The material used to construct the walls can be wood
or stone. In both cases, gaps or openings are construc-
ted to facilitate ventilation. When wood boards are used
to construct the side walls, they are placed vertically
and separated by about 1-2 cm, forming narrow openings.
In stone walls, the gaps are formed because the stone
blocks do not fit perfectly together.
There are different types of hórreos according to the
characteristics of the parts described above. This study
aimed to analyse a particular type, the Mondoñedo
hórreo, which is found in the towns of the coastal area
near the Cantabrian Sea in the province of Lugo (Figs. 1
and 2).
This is a mixed type in which wood and stone are used.
It has a rectangular layout with a prismatic grain chamber.
The width and height of the chamber tend to be similar
in all hórreos, while the length varies from one to another.
The chamber rests on the feet but is separated from
them by an element of stone (usually flat) designed to
prevent rodents from accessing the chamber («tor-
narratos» in the Galician language, a word derived
from «tornar», turn off, and «ratos», mice). The chamber
floor can be made of wood or stone (slate or granite).
The roof structure consists of a wooden beam at the
ridge. There may or may not be intermediate beams that
support this piece. The rafters are supported on the ridge
beam and the beam located at the top of the wall. This
beam is part of the structure of the beams and columns
of the chamber. The roofing material is usually slate.
The walls are made of wooden boards with a slight
separation between them. The front walls can be made
of continuous granite or stone masonry. In one of the
front walls, there is an access door to the grain chamber;
if the access door is not in this position, it is located
in one of the side walls.
Selection of the hórreos to study
The selection of the hórreos to study was based on
a previous study done by the authors in which all of
the Mondoñedo-type hórreos of Galicia were invento-
ried (1,656 in total). This inventory included the cons-
truction features, location and orientation of each one.
In the first phase, a selection among all the hórreos
in the inventory was done, retaining those with the
following features: no construction deficiencies,
currently in use and having all of the structural charac-
teristics typical of a Mondoñedo-type hórreo without
later additions. Among the buildings selected in this
phase, a second selection was done, forming groups
of those with different geographic locations (inner
zone, coast and intermediate), altitudes (valley or
mountain) and wind exposures (normal or high expo-
sure). From this group of hórreos, three were chosen
for which the cooperation of the owners permitted
more reliable data collection. In the text, they will be
referred to as hórreos number 1, number 2 and number 3.
Their specific geographic locations are shown in
Figure 3 and their descriptive data are listed in Table 1.
The building features were similar across the three
examples, including their height from the ground. The
open area for ventilation in the longitudinal side walls
was 11% of the total area of these walls. The ratio of
height to width ranged between 1.4 and 1.7. Three
hórreos with similar building features were selected
Evaluation of traditional grain store buildings (hórreos) in Galicia 927

928 O. A. Pérez-García et al. / Span J Agric Res (2010) 8(4), 925-935
Figure 1. Parts of a Mondoñedo-type hórreo: a) three-dimensional view, b) layout, c) front view and d) section. Source of dra-
wings: De-Llano (1983).
1
2
3
4
5
6
7
8
9
10
11
12
13
1
8
7
11
10
9
13
2
4
3
5
10
12
1011
a)
b)
c) d)
Front
view
Key Galician language Spanish English
1 Sobrepena Vierteaguas Overhanging eave
2 Cubrición de lousas Cubierta de pizarra Roof covering of slates
3 Cume Cumbrera Ridge
4 Tixeira Viga de cubierta Rafter
5 Bagalustos Tablas de cerramiento Closing boards
6 Cinta Travesaño Wall girt
7 Soleiras Viga de alero Eave beam
8 Peche do penal Hastial Gable end
9 Trabes Viga de solera Floor beam
10 Piso Piso Floor
11 Colunas Pilares Columns
12 Cepas/tornarratos «Desvía-ratones» Flat stone to keep off rodents
13 Pes Pies/bases Feet
12 5
Figure 2. A Mondoñedo-type hórreo: a) outdoors: 2) roof covering of slates, 5) closing boards, 6) wall girt, 7) eave beam, 9) floor
beam, 11) columns, 12) flat stone to keep off rodents, 13) feet and 14) roof decoration stones; and b) indoors: 4) rafter, 15) ridge-
piece, 16) wood board roof sheeting to support slates and 17) back wall.
a) b)

to facilitate analysis. The differences among them were
in their geographic and topographic features related to
the places where they were built (geographic location,
topographic altitude, degree of exposure to the wind)
and the direction of their longitudinal axes.
Selected and examined variables
RH and air T were measured both indoor (i) and out-
door (o) the chambers of the hórreos. The measure-
ments were taken in hórreo number 1 during the
summer of 2006 (from 1st August to 30th September)
and in hórreos number 2 and number 3 during the
autumn of the same year (from 1st October to 30th No-
vember). Because of the time schedule chosen in the
study, details for 168 days were obtained. All measu-
rements were made with empty hórreos.
Three daily measurement periods were established,
morning (m), afternoon (a) and night (n), with the aim
of capturing the fluctuations in temperature and
humidity during both sunlight and night periods. These
periods were defined as follows: night period (from
midnight to 11:00), morning period (from 11:00 to
16:00) and afternoon period (from 16:00 to 24:00).
Three characteristics of each of the environmental
parameters were recorded during these periods: a current
measurement (c), the parameter’s value at the time of
Evaluation of traditional grain store buildings (hórreos) in Galicia 929
Figure 3. Geographical locations of the studied hórreos: a) Galicia and b) locations of the hórreos in the coastal area of Lugo.
France
Galicia
Spain
Portugal
Portugal
Lugo
a) b)
Table 1. Features of the studied hórreos
Feature
Hórreo
Number 1 Number 2 Number 3
Geographical location
Degree of wind exposure
Topographic altitude, m
Direction1
Dimensions
Length, m
Width, m
Height2, m
Material of structural elements3
Roofing material
Lateral wall closure
Midway between the
mountains and coast,
10 km from the coast.
Municipality of
Mondoñedo
Exposed
140
NW-SE
4.30
1.20
2.00
Coastal, close to the coast.
Municipality of Foz
Normal
60
N-S
5.20
1.30
2.15
Midway between the
mountains and coast, 10 km
from the coast. Municipality
of Mondoñedo
Exposed
120
E-W
5.00
1.45
2.00
Granite stone
Slate
7-cm wide wooden boards separated by 1 cm
1Direction of the longitudinal axis of the hórreo.2Eave height. 3Columns, front walls, floor beams and bases («feet»).

reading (at 9:00, 14:00 and 21:00); the maximum mea-
surement (max), the maximum value during the period;
and the minimum measurement (min) or the minimum
value during the period. In each hórreo, nine measure-
ments were taken inside and another nine outside, three
for each time period, for both RH and T. Therefore,
there were 18 study variables for RH and the same
number for T.
To carry out measurements, two thermo-hygrometers
were used, one situated inside the chamber and the
other outside. These devices have one central unit that
can measure T and air RH. They also have an internal
memory that enabled data to be stored and provided
maximum and minimum values for a specific period.
The sensitivity was ± 1° for T and ± 0.1% for RH.
The data obtained for environmental variables were
analysed using SPSS version 17. First, the means were
compared to determine if there was a difference
between outdoor and indoor variables (using a t-test
for normally distributed variables and Mann-Whitney
test for the others). The significance level was set at
0.05. Linear regression analyses were conducted to
determine correlations between the indoor and outdoor
variables. Finally, a factor analysis was performed to
confirm the existence of correlated homogeneous groups
within the examined variables. KMO and Bartlett tests
were run in order to determine the usefulness of the
factor analysis. A compromise solution was used to
select the number of factors based on the percentage
of variance explained (~80%) combined with screen
plot information. Different rotation methods were
attempted and the oblique rotation method was chosen
to better achieve well-defined factors.
Results
A total of 168 measurements were made of each of
the variables studied. Half of the variables correspond
to the RH and the other half to T. Figures 4a and 4b
show their averages and Figures 4c and 4d show the
average differences between the maximum and
minimum measurements taken indoors and outdoors.
Hórreo 1 was in an interior location, where it was ex-
posed to the wind; measurements were taken during
the summer. There were significant differences between
930 O. A. Pérez-García et al. / Span J Agric Res (2010) 8(4), 925-935
a)
c) d)
b)
60
65
70
75
80
85
90
95
100
Maximum relative
humidity
Minimum relative
humidity
Actual relative
humidity
Average relative humidity (%)
Time period
Outdoor measurement Indoor measurement
0
5
10
15
20
25
Night Morning Afternoon
Maximum relative humidity less minimum
Average between maximum
and minimum humidity,
outdoors and indoors (%)
0
5
10
15
20
25
Maximum
temperature
Minimum
temperature
Actual
temperature
0
5
10
15
20
Night Morning Afternoon
Maximum temperature less minimum
Night
Morning
Afternoon
Night
Morning
Afternoon
Night
Morning
Afternoon
Night
Morning
Afternoon
Night
Morning
Afternoon
Night
Morning
Afternoon
Average temperature (°C)
Average between maximum
and minimum temperature,
outdoors and indoors (°C)
Time period
Outdoor measurement Indoor measurement
Time period
Outdoors Indoors
Time period
Outdoors Indoors
91.7
85.7
92.3 90.1
84.0
75.8 76.9
75.0
72.0
67.1
76.2
79.4
85.7
71.6
76.8
88.6
81.3
87.0
15.8
18.1 18.3
13.3 13.4
17.6
17.2
12.3
15.5 15.7
15.3
15.1
12.1
17.0
13.2
13.2
17.9
16.3
3.8 4.8
3.2
4.0 4.1
2.4
14.9
20.5
17.0
12.4 13.0
10.4
Figure 4. Characteristics of the variables according to time periods of study: a) average relative humidity, b) average temperature,
c) average difference between maximum and minimum relative humidity and d) average difference between maximum and mini-
mum temperature.

the maximum relative humidities outside and inside
the hórreo, based on the Mann-Whitney test, at night
(Z = –3.611, p<0.05) and in the morning (Z = –6.268,
p< 0.05). As regards the minimum RH (RHmin), there
was only a significant difference between measurements
taken outdoors and indoors at night (t =4.243, p< 0.05).
Hórreo 2 was in a coastal location with normal ex-
posure to the wind; measurements were taken in the
autumn. As for the previous hórreo, there were signifi-
cant differences between the maximum RH (RHmax)
outdoors and indoors, based on the Mann-Whitney test,
at night (Z = –5.982, p< 0.05) and in the morning
(Z = –4.036, p< 0.05). There was significant difference
in the afternoon period (t = –2.661, p=0.009). However,
there was no significant difference between the RHmin
measurements recorded outside and inside the hórreos
during the different periods.
Hórreo 3 was in an interior location between the moun-
tains and the coast, where it was exposed to the wind; mea-
surements were taken in the autumn. As for the previous
hórreos, there were significant differences between the
RHmax measurements outdoors and indoors based on
the Mann-Whitney test, at night (Z =–5.778, p< 0.05)
and in the morning (Z =–4.938, p< 0.05). There were
also significant differences in the afternoon between
the exterior and interior both for the RHmax (t =–4.111,
p< 0.05) and for the RHmin (t = –1.985, p= 0.05).
There were significant differences between indoor
and outdoor RH variation (difference between RHmax
and RHmin) in the three studied periods according to
Mann-Whitney tests (night Z =–4.021, p< 0.05; morning
Z =–4.584, p< 0.05; and afternoon Z =–7.174, p< 0.05).
When analysing the current measurements taken at
9:00, 14:00 and 21:00 hours both inside and outside
the hórreos, it was observed that the RHi could be esti-
mated from the outdoor RH (RHo). The regression line
between the current RHi and current RHo is given by
Equation [1]:
[1]
where y= RHi, x= RHo and D1and D2are dummy va-
riables (D1= 1 when the measurement was taken at
14:00 and D1= 0 in other cases; D2=1 when the measure-
ment was taken at 21:00 hours and D2=0 in other cases).
The coefficients are statistically significant (t = 44.272,
t =4.614, t = –4.370 and t= 12.577, respectively; p< 0.05
in all cases) and the correlation coefficient (coefficient
of determination) is R2= 0.827.
Figure 5 shows the regression lines; in this graph,
the effects of the different times at which the current
measurements were taken can be observed. For a spe-
cific value of RHo, the RH inside the hórreo was lower
at 21:00 than at 9:00 hours and this was lower than at
14:00 hours.
With regard to T, there were no significant differen-
ces in any period or hórreo between the outdoor
minimum T (Tmin) and the indoor Tmin. There were
significant differences in the maximum T (Tmax) bet-
ween outdoor and indoor measurements only in hórreo
number 1 at night (t = –2.787, p= 0.006).
We determined the differences between the maximum
and minimum T inside and outside the hórreos in each
of the time periods and compared them. There were
significant differences between the outdoor T (To) and
indoor T (Ti) in the morning and afternoon periods
based on the Mann-Whitney test (morning Z = –4.454,
p= 0.014; afternoon Z =–4.853, p< 0.05).
By analysing the current T measurements both
inside and outside the hórreos, it was possible to
estimate Ti from the data obtained outdoors. The
regression line for the relation between the Ts mea-
sured inside and outside the hórreos is shown in
Equation [2]:
[2]
where y= Ti, x= To and D1and D2are dummy variables
(D1= 1 when the measurement is made at 16:00 and
D1= 0 in other cases; D2= 1 when the measurement is
performed at 9:00 hours and D2= 0 in other cases).
The coefficients are statistically significant (t =
95.612, t = –9.028, t =–7.794 and t = 6.961, respecti-
y=0.95⋅x+0.94 ⋅D1−0.80 ⋅D2+1.17
y=0.74 ⋅x+2.29 ⋅D1−1.93 ⋅D2+19.28
Evaluation of traditional grain store buildings (hórreos) in Galicia 931
50
55
60
65
70
75
80
85
90
95
100
50 55 60 65 70 75 80 85 90 95 100
Outdoor current relative humidity (%)
Indoor current relative humidity (%)
Regression line of measurements at 9:00
Regression line of measurements at 14:00
Regressioin line of measurements at 21:00
Figure 5. Linear regression between the outdoor and indoor ac-
tual measurements of relative humidity.

vely; p< 0.05 in all cases) and the regression coefficient
is R2= 0.955.
Figure 6 shows the regression lines where the effect
of the time at which the measurement was taken can
be observed. For a specific value of To, the value of
the T reached inside the hórreo was lower when the
measurement was performed at 21:00 than when it was
performed at 14:00 or 9:00. The Ts inside the hórreo
were practically the same at 9:00 and 14:00.
Two T-RH graphs for two 24-hour measurement
periods are shown in Figure 7; they were randomly
chosen from among the graphs available. The hórreos’
moderating effect on indoor air conditions is noticeable
at both low (Fig. 7a) and high (Fig. 7b) RHo.
The previous results showed that the building cha-
racteristics of hórreos influenced the maintenance of
indoor environmental parameters; however, the magni-
tudes of the differences between the inside and outside
environment were variable. Owing to the fact that the
building features of hórreos were similar while their geo-
graphic and topographic conditions differed, the analy-
sis must take into account the influences of the hórreos’
geographic and topographic features. These features
were geographic location, topographic altitude, degree
of exposure to the wind and the direction of the buil-
ding’s longitudinal axis; they are shown in Table 1.
The differences between indoor and outdoor T and
RH measurements were quantified. Nine T and nine
RH variables (for the three types of measurements, ma-
ximum, minimum and current; and for the three time
periods, night, morning and afternoon) were analysed.
A factor analysis was used to determine the existence
of homogeneous groups of closely correlated variables.
In the case of T differences, five components were
identified, accounting for approximately 83% of the
total variance (Table 2). The weights of each of these
factors are very similar.
In the case of the RH difference, four components
were identified, accounting for approximately 80% of
the total variance (Table 2). Two factors accounted for
approximately 60% of the variance; this reveals the
existence of groups of correlated variables when the
differences between outdoor and indoor measurements
are studied.
Discussion
Hórreos have traditionally been used successfully
for drying and storage of cereal grains, in this case mai-
932 O. A. Pérez-García et al. / Span J Agric Res (2010) 8(4), 925-935
4
6
8
10
12
14
16
18
20
22
24
26
4 6 8 101214161820222426
Outdoor current temperature (ºC)
Indoor current temperature (ºC)
Regression line of measurements at 9:00
Regression line of measurements at 14:00
Regression line of measurements at 21:00
Figure 6. Linear regression between the outdoor and indoor
actual measurements of temperature.
10
12
14
16
18
20
22
24
26
Temperature (ºC)
35
40
45
50
55
60
65
70
75
Night
period
Morning
period
Afternoon
period
0:00 11:00 16:00 24:00
10
12
14
16
18
20
22
24
26
Temperature (ºC)
60
65
70
75
80
85
90
95
100
Night
period
Morning
period
Afternoon
period
0:00 11:00 16:00 24:00
Relative humidity (%)
Relative humidity (%)
Time periods
Indoor temperature Outdoor temperature
Indoor relative humidity Outdoor relative humidity
Figure 7. Example of the damping effect of the hórreo on environmental conditions of indoor air: a) low and b) high outdoor re-
lative humidity. Graphs are shown for two 24-hour periods.
a) b)

ze. Technical recommendations for this cereal suggest
that to reduce its moisture content from around 24% to
preserving values of around 12 to 14%, it is necessary
that the grain be exposed to air with a RH between 60
and 75%. Across RH intervals of RH≤60%, 60% < RH≤
75%, 75% <RH ≤85% and 85% <RH ≤100%, variation
was observed in the percentages of measurements
within each interval that were favourable for the sto-
rage of maize. For outdoor measurements, the interval
85%<RH≤100% represented 50.21% of all of them,
the interval 75% < RH ≤85% 19.44% and the interval
60% < RH ≤75% 23.41%. For the measurements inside
the hórreos, the percentage of the highest interval
decreased and the percentages of the others increased
(36.54%, 32.46% and 26.86%, respectively).
Figures 4a and 4b show the average values of the
variables. Note that if the RHo was high, the indoor
humidity was lower and vice versa. The maximum RHo
decreased from 3.7 to 4.7% inside the hórreo and the
minimum rose from 0.7 to 4.5% depending on the time
period. The T variation was less marked and was in the
range of 0.1-0.9°C.
The variation of the RH indicates a softening effect
of hórreos on the conditions of the outdoor air entering
the building. The highest and lowest outdoor values
were smoothed indoors. When the RHo was greater
than or equal to 90%, the RHi was, on average, 5.2%
lower. If the RHo was less than or equal to 65%, the
indoor humidity was, on average, 3.2% higher. This
effect diminished as the outdoor humidity approached
the mean. When the RHo was around 75%, this effect
was smallest and it increased in magnitude when the
humidity deviated from this value.
The analysis of RH in each of the hórreos for each
measurement type (maximum, minimum and current)
and time period (night, morning and afternoon) showed
that the three hórreos behaved similarly. The maximum
relative humidities indoors and outdoors were signifi-
cantly different for most of the time periods, while the
minima were not, except in one case.
Evaluation of traditional grain store buildings (hórreos) in Galicia 933
Table 2. Factor analysis of the temperature and relative humidity differences between outdoor and indoor air (oblique rotated
factor matrix, n =168)
Factor loadings
Communality Mean score
1234 5
Items of temperature
t_d_m_max 0.86 –0.03 –0.10 –0.03 –0.10 0.78 0.85 ± 0.89
t_d_m_c 0.85 –0.17 0.20 0.15 0.17 0.78 0.61 ± 0.93
t_d_a_max 0.61 0.36 –0.25 –0.34 –0.12 0.77 0.42 ± 0.70
t_d_a_c –0.15 0.92 –0.01 –0.11 0.09 0.88 –0.47 ± 0.62
t_d_a_min 0.06 0.81 0.16 0.35 0.04 0.83 –0.41 ± 0.69
t_d_n_c 0.01 –0.04 –0.91 0.06 –0.03 0.82 0.26 ± 0.74
t_d_m_min –0.03 –0.07 –0.88 0.10 0.15 0.80 0.18 ± 0.76
t_d_n_max 0.03 0.11 –0.18 0.91 –0.08 0.86 –0.39 ± 1.29
t_d_n_min 0.03 0.10 –0.11 –0.09 0.96 0.96 –0.20 ± 0.41
% of variance 22.94 20.25 17.78 12.09 9.95 83.03
Items of relative humidity
rh_d_n_min 0.90 0.00 –0.08 –0.13 0.72 2.72 ± 5.16
rh_d_n_c 0.78 –0.02 0.02 0.27 0.81 4.25 ± 4.99
rh_d_m_max 0.67 0.09 0.26 0.07 0.72 3.52 ± 3.49
rh_d_m_c –0.05 0.93 0.04 –0.06 0.85 –2.02 ± 5.51
rh_d_m_min 0.04 0.92 –0.04 –0.02 0.85 –3.69 ± 5.99
rh_d_a_min 0.00 0.80 –0.01 0.06 0.65 –2.15 ± 6.08
rh_d_a_max –0.03 –0.03 0.95 –0.04 0.86 4.57 ± 4.10
rh_d_a_c 0.04 0.02 0.90 0.02 0.84 4.61 ± 3.85
rh_d_n_max 0.01 0.00 –0.11 0.98 0.96 5.24 ± 3.51
% of variance 36.63 21.64 13.80 8.64 80.70
Item abbreviations: t, temperature; rh, relative humidity; d, difference between the outdoor measurement and the indoor measure-
ment; m, morning period; a, afternoon period; n, night period; c, current measurement; max, maximum measurement in the period;
min, minimum measurement in the period.

Figure 4c shows the average of the differences bet-
ween the maximum and minimum RH indoors and out-
doors. The analysis of these differences for each varia-
ble and time period revealed significant differences bet-
ween the outdoor and the indoor measurements in all
cases. The difference between the maximum and mini-
mum RH indoors was, on average, 5.4% smaller than
the difference outdoors. Therefore, the fluctuations in RH
inside the hórreos were smaller than they were outside.
The current RHi was highly correlated with the
current RHo. Figure 5 shows the regression lines, from
which the effect of the time period in which the
measurement was made can be seen. With regard to the
RH outdoors, the RHi was lower at 9:00 and at 21:00.
This suggests again that inside the hórreo there was a
buffering effect of variations of external RH. This
effect could be held to natural ventilation; according
to Lomas (2007) geometric design is one of the pro-
cesses by which natural ventilation can be guaranteed.
For example, roof features are important (Özdeniz and
Hançer, 2005) and can be used for maintaining appro-
priate ambient conditions, such as humidity (Abaza,
2005). Nantka (2006) explains that traditional struc-
tures that allow natural ventilation can be used in
the design of new buildings or in the restoration of exis-
ting ones.
With regard to T, there were no remarkable differen-
ces between indoor and outdoor values measured in
the hórreos. Figures 4b and 4d show the average T and
the average of the differences between the maximum
and minimum T indoors and outdoors. It was noted that
the variations were smaller for T than in the case of RH.
There was no significant difference between the
indoor and outdoor maximum or minimum Ts for any
period, except for the Tmax of hórreo number 1 at night.
As for the difference between maximum and mini-
mum Ts indoors and outdoors, it was found that the va-
riation differed significantly between the inside and out-
side during the morning and afternoon, but not at night.
The current Ti of the hórreo also showed a high
correlation with the current To. Figure 6 shows the
regression lines for the different time periods. The
greater slopes of these lines in relation to those for RH
indicate the similarity between indoor and outdoor T.
A buffering effect of the hórreo on T can also be
considered, but to a lesser extent than in the case of
RH. The stack effect due to temperature and wind
pressure are two of the main factors that, also combined
with the design of the building, guarantee natural
ventilation (Khan et al., 2008; Larsen and Heiselberg,
2008). In this study, the effect of temperature is less
relevant.
Because of their configuration, hórreos are effective
buildings for RH and T control. Inside, oscillations of
RH are damped and, to a lesser extent, oscillations of
T are also damped. In conclusion, it can be noted that
these two parameters remain more stable within the
studied hórreos than outside of them.
Because the construction characteristics of the stu-
died hórreos were similar and they were empty, this
study can be extended by analysing the environmental
parameters in hórreos with different amounts of grain
inside. Considering that the building materials them-
selves can influence buildings’ thermal performance
(Parra-Saldivar and Batty, 2006), it can also be exten-
ded to hórreos built with other materials (for example,
entirely of stone).
Once the influences of the construction characte-
ristics on environmental parameters were determined,
the final part of the analysis was to determine whether
any factor could explain the variability of these para-
meters. These factors may be related to the differences
between the studied hórreos related to geographical
and topographical characteristics (i.e., geographical
location, topographic altitude, degree of exposure to
the wind and the direction of the building’s longitudinal
axis). These factors could be considered as outdoor air
factors that can also be taken into account to evaluate the
potential for natural ventilation (Germano and Roulette,
2006) such as the wind’s incidence angle (Larsen and
Heiselberg, 2008). The evaluation of ventilation
together with other factors, like the outdoor air charac-
teristics, allows to predict the energy and hygrothermal
performance of buildings (Freire et al., 2008) or assess
their energy efficiency (Tzikopoulos et al., 2005).
The factor analysis of the difference between indoor
and outdoor T identified five components (explaining
83% of the total variance, Table 2), but the weights of
each are very similar and no clear interpretation can
be made. This suggests that the influences of the various
above-mentioned conditions were minimal for all of
the T measurements taken (maximum, minimum and
current) and for all time periods.
In the case of RH, the factor analysis identified two
components (explaining 60% of the total variance,
Table 2). Factor 1 represents low-humidity conditions
at night (i.e., during low T) and has the greatest weight
(36.6%). Factor 2 represents conditions of low diurnal
humidity (i.e., during medium and high T) and has a
lesser weight (21.6%).
934 O. A. Pérez-García et al. / Span J Agric Res (2010) 8(4), 925-935

The building configurations of hórreos create signi-
ficant differences in the indoor conditions relative to
the outdoor ones. When the humidity is high, the in-
fluence of geographic and topographic conditions on
the magnitudes of these differences is minimal. That
is, inside the hórreos, there is a similar reduction of
the outdoor RHmax. By contrast, the factors described
are indicative of the fact that the RHmin reached inside
the hórreo does not depend only on its constructive
characteristics. The dissimilar features of the studied
hórreos in terms of their geographic and topographic
conditions could be the origin of the existence of these
factors. Consequently, the magnitude of the variation
of RHmin inside the hórreo with respect to the outdoor
humidity is also conditioned by the geographic location,
topographic altitude, degree of exposure to the wind
and direction of the building’s longitudinal axis. In
order to be able to establish more precisely the nature
of the variation that can cause geographic and topogra-
phic conditions of hórreos to affect the indoor air, a
more detailed study is necessary.
Acknowledgements
The authors thank the hórreos’owners for allowing
access to the buildings studied in this paper.
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