Sectional concrete garages and condensation.

[Philip Stokes]

I am currently considering replacing a nearly 50 year old precast concrete single garage with a double garage of similar construction.

I am however, concerned about the possibility of condensation, particularly as my main reason for replacing the garage is to enable me to house a (valuable to me) classic car, that is currently garaged elsewhere - as well as my everyday vehicle.

I have read various comments in archived posts regarding these type of garages, but I have to say that my existing garage, which has a flat, corrugated asbestos panel roof, has never suffered from condensation, and always been quite dry inside, although a couple sections of the roof are now leaking at joints when it rains.

I have been looking at the Compton and Mayfair ranges of garages. I am inclined more towards the Compton range purely on the basis that the range of options available, including door sizes and security options, is more comprehensive than the Mayfair range.

Both manufacturers offer garages with apex roofs, constructed with trusses and purlins carrying a felted and tiled roof. However, the Mayfair roof is tiled with interlocking concrete tiles and utilises the Marley "Dry Verge" and "Dry Ridge" ventilation systems -

- whilst the Compton roofs are tiled with granulated steel roof tiles. I don't know much about these tiles, except that they seem to be a fairly modern invention and appear to be quite prevalent on houses in the US and Australia.

I am concerned however that a steel tiled roof may be more prone to condensation. Even if the roofing felt were to remain moisture free on the underside - surely water is likely to form on the underside of the tiles and eventually rot the wooden battens to which the tiles are attached?

Whichever type of garage I choose, I am considering installing additional vents in the gable end facia at the front of the garage, with a couple of humidistat controlled fans similarly positioned in the rear facia, to increase ventilation through the building. I have one of these fans in a shower room in the house, and it is very effective.

My car currently lives in an Airflow Airchamber, in an unheated lean-to garage with pebble-dashed single brick walls, and a leaky slate tiled roof with no felting. (For anyone not familiar with the Airchamber, it is a plastic enclosure completely surrounding the car, with a couple of

12 volt fans running from a mains transformer, that continuously circulate air within the chamber - the theory being that the air within the chamber is kept above the dew point, preventing condensation on the vehicle within.) I have had this chamber for nearly three years and I have to say it performs brilliantly. I will still be using it within the new garage.

I would appreciate any comments on the two choices of roof construction, particularly from anyone who has experience of either type of garage, and also the likely effectiveness of my proposed use of fans to draw air through the building.

I know the erection of the garage itself is not strictly a DIY question, but I cannot afford to pay a builder to construct a brick built garage (around 35-40,000 pounds in this part of the country!) and I have neither the time or bricklaying skills to attempt it myself.

All thoughts greatly appreciated.

Phil

[Paul - xxx]

Philip Stokes posted:

Not too much of a problem then, really .. ;)

Ventilation is everything to keeping condensation at bay. IMHO neither roof will have any significant differences from the other, especially with the ventilation you describe .. ;)

[Richard]

I have a sectional concrete construction double garage with old fashioned corrugated asbestos concrete roofing. Normally as dry as a dog's bone but under certain weather conditions a small amount of condensation forms inside the roof sheets which drips down. My solution to keep everything inside in pristine condition is to cover them with cotton or linen sheeting. As well as absorbing and disbursing the odd drips it keeps the dust off and eliminates spider and fly droppings. It is also very cost effective!

Richard.

[Mark S.]

snip

I have/had a Compton one for some years, single with no door or window just the two part metal front door and a metal sheet roof.

The location meant it would have been less secure with extra windows and a door etc.

The roof gets some condensation on it which tends to run so far then drips onto the car etc. The roof now has some "white" calcium type marks on it but it's still water tight and in one piece etc.

Only "mistake" was to lay my own slab which was just about ok but they said it was out a bit at one end so wouldn't use it without them putting another lay on top of it due to the guarantee they offer etc.

Mark S.