"Philip Stokes" wrote in message
...
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 -
http://www.marleyroofing.co.uk/content/30.chtml - 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

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.