Great resource on mold and crawlspaces and also on mold particles and flow throughout a building envelope. (in cold climates, esp. but much is applicable everywhere)..

[Guest guest]

This is an extremely useful but also extremely technical doctoral

dissertation that proves a number of important things about mold inside of

buildings..

The link at article #6 is extremely important because it shows how the very

finest particles tend to propagate throughout a wooden building..

Worth downloading!

Even if you don't understand the math..

http://lib.tkk.fi/Diss/2003/isbn9512267756/

Moisture and Fungal Spore Transport in Outdoor Air-Ventilated Crawl Spaces

in a Cold Climate

Miimu Airaksinen

Dissertation for the degree of Doctor of Science in Technology to be

presented with due permission of the Department of Mechanical Engineering

for public examination and debate in Auditorium K216 at Helsinki University

of Technology (Espoo, Finland) on the 21st of November, 2003, at 12 o'clock

noon.

Overview in PDF

format<http://lib.tkk.fi/Diss/2003/isbn9512267756/isbn9512267756.pdf>(ISBN

951-22-6775-6) [1510 KB]

Dissertation is also available in print (ISBN 951-22-6771-3)

Abstract

A crawl space foundation is widely used in buildings and detached houses in

northern countries. The relative humidity of the air in crawl spaces is the

most critical factor concerning mould growth in the structures of a crawl

space. Possible contamination in the crawl space might be transported

indoors if the pressure inside the apartment is lower. The objective of the

study was to find out the important properties of ground covers and the

optimal air change rates for the controlling of moisture conditions in an

outdoor air-ventilated crawl space in a cold climate and to estimate the

acceptability of current moisture conditions in respect of material

durability. In addition, factors affecting the transport indoors of possible

pollutants from crawl spaces were studied.

The moisture conditions were calculated with a dynamic simulation model,

which was validated against measured data. The moisture and thermal capacity

and resistance of the ground cover were varied, as was the air change rate

in the crawl space. The acceptability of moisture conditions was evaluated

using a mould growth index. The concentration of fungal spores was measured

both through field measurements and full-scale laboratory measurements. The

penetration of inert particles of different sizes through a building

envelope was studied by means of full-scale laboratory measurements. The

airtightness of the building envelope and the pressure difference across the

envelope were varied.

It was shown that in a relatively warm crawl space moisture problems were

easy to avoid – ground soil should be covered so as to prevent moisture flow

from the ground and an air change of at least 0.5 ach is enough to keep

relative humidity at a low level. A relatively cold crawl space needs a

ground cover with moisture and thermal resistance. A ground cover with a

moderate thermal resistance, such as 15 cm lightweight aggregate, needs a

higher ventilation rate, at least 2.0 ach, to warm up the crawl space in the

summer. A ground cover with a high moisture capacity can stabilise the

fluctuation of relative humidity in a crawl space, and thus avoid critical

peaks of relative humidity in respect of mould growth. The safest ground

cover solution is a thick cover with a high thermal resistance and a low air

change rate of 0.5 ach; with this approach natural ventilation can be used.

Heating a crawl space in summer is an excellent way to avoid mould growth.

The advantage of heating is greatest if the ground cover has a high thermal

conductivity. The energy consumption of heating is strongly dependent on the

set point value for the relative humidity. However, if the set point value

is kept reasonable and the ventilation rate remains low the specific annual

energy consumption is within the range of 1.4-3.6 kWh / m2 of the crawl

space area.

Results from field measurements showed a correlation between microbes in the

crawl space and indoors. In the full-scale laboratory measurements it was

established that inert particles and fungal spores in a size range 0.6-2.5

µm penetrate a wooden structure at moderate pressure differences. Laboratory

measurements showed that the penetration was highly dependent on pressure

difference and not dependent on holes in the surface boards of the

structure. The results are likely to show that the surface contacts of

mineral wool in the floor structure may have an important role in

penetration. It is clearly difficult to control the penetration of fungal

spores by sealing the building envelope. The only effective way to avoid

penetration seems to be balancing the building; however, in cold climates

the moisture condensation risk should be taken into account. The results

indicate that mechanical exhaust ventilation causing an under-pressure in

the building may cause health risks if some contamination exists in the

building envelope.

This thesis consists of an overview and of the following 6 publications:

(LINKS AT THESE URLS:

1. http://lib.tkk.fi/Diss/2003/isbn9512267756/article1.pdf

2. http://lib.tkk.fi/Diss/2003/isbn9512267756/article2.pdf

3. http://lib.tkk.fi/Diss/2003/isbn9512267756/article3.pdf

4. http://lib.tkk.fi/Diss/2003/isbn9512267756/article4.pdf

5. http://lib.tkk.fi/Diss/2003/isbn9512267756/article5.pdf

6. http://lib.tkk.fi/Diss/2003/isbn9512267756/article6.pdf

7. http://lib.tkk.fi/Diss/2003/isbn9512267756/index.html

8. http://lib.tkk.fi/Diss/2003/isbn9512267756/isbn9512267756.pdf

)

1. Kurnitski J. and Matilainen M., 2000. Moisture conditions of outdoor

air-ventilated crawl spaces in apartment buildings in a cold climate. Energy

and Buildings 33, No. 1, pages 15-29. © 2000 Elsevier Science. By

permission.

2. Airaksinen M., Kurnitski J. and Seppänen O., 2003. On the crawl space

moisture control in buildings. Proceedings of the Estonian Academy of

Sciences: Engineering 9, No. 1, pages 34-58. © 2003 Estonian Academy

Publishers. By permission.

3. Matilainen M. and Kurnitski J., 2003. Moisture conditions in highly

insulated outdoor ventilated crawl spaces in cold climates. Energy and

Buildings 35, No. 2, pages 175-187. © 2003 Elsevier Science. By permission.

4. Matilainen M., Kurnitski J. and Seppänen O., 2003. Moisture conditions

and energy consumption in heated crawl spaces in cold climates. Energy and

Buildings 35, No. 2, pages 203-216. © 2003 Elsevier Science. By permission.

5. Airaksinen M., Pasanen P., Kurnitski J. and Seppänen O., Microbial

contamination of indoor air due to leakages from crawl space – a field

study. Indoor Air, accepted for publication. © 2003 by authors and © 2003

Blackwell Publishing. By permission.

6. Airaksinen M., Kurnitski J., Pasanen P. and Seppänen O., Fungal spore

transport through a building structure. Indoor Air, accepted for

publication. © 2003 by authors and © 2003 Blackwell Publishing. By

permission.

Keywords: crawl space, mould growth, moisture control, ground covers,

ventilation

This publication is copyrighted. You may download, display and print it for

Your own personal use. Commercial use is prohibited.

© 2003 Helsinki University of Technology