condensation free garage roof suggestions

[knockavacca]

hi i want to replace my steel courragated garage roof,because of the condensation problems,can anyone suggest a roofing material that mite be suitable, i have seen some courrageted sheets in my local diy store, "like black bituman or something" ive no idea if they would be suitable,the garage size is approx 20 foot by 12,any suggestions would be appreciated thanks

[douglas9401]

If the existing is sound I'd wait till it's dry and spray foam the underside.

[brenda]

I fastened sheets of polystirene (sp) to the underside of my garage roof -- worked well.

[knockavacca]

thank you both for your suggestions, i had to treat my roof last year because it had started to rust,and im afraid it was not entirely succesful, so i think it will have to be replaced, ??? but with what ???thanks again

[buildersmate]

The thing about steel sheds is that they do not allow water vapour to percolate through the roof - steel isn't porous as a felt/tile roof is.
So, depending on what activities you do in there (that are the source of water vapour) you cannot eliminate this problem.
As the first two respondents point out, if you insulate the underside, you will raise the temperature at the underside of the insulating surface and this may effectively eliminate the problem.
Unless this has been going on for donkeys' years, it is unlikely that the roof has rusted through through - corrugated iron generally lasts more than 25 years.

[knockavacca]

many thanks for all your advice ,i will look at spraying the inside as advised,any suggestions about which product to use would be helpful cheers

[The Builder]

Here's something I did on a shed that I wanted to include in my workshop ........... save yourself a job, and leave the existing roof in place. Lay timber bearers across it to fix new sheets to. Fit insulation (Celotex/Kingspan between the timbers to create a "warm roof". Fix the new sheets over the whole thing.
Use "box profile" sheets........ that's thin steel sheets with a very durable powder-coated paint finish. (Corrugated, but with a squarish section.)
Or ......... "Onduline" is easy to cut and work with ....... with a decent green shed-like finish.
You'll raise the surface temp of the existing, as BM has explained. The existing will also act as a "vapour check" ........ preventing vapour from passing through the insulation and condensing under the new sheets.
You'll have to raise the guttering, and alter the verge profile all round. You will then have something reasonably attractive that'll last for years.

[knockavacca]

thanks MARK thats what ill have a go at in the new year , thanks to all

[Runeoth]

a good classic solution is wood. create a frame out of some good 2x1, lay an MDF (i think) layer over the top and then bitumen and felt. can then use insulation for warmth and then plasterboard to cover. will create an 'inside' feel. plus if you have a light in there you will be able to hide the wires in the cavity. add a slight incline to the roof and some guttering and you should have many years of dry garage!

[Runeoth]

if its within the budget that is