Flat roof insulation - is it better to get it on top of the roof, or to take ceilings down and do from within?

Question

We have a flat roof, which needs replacing. one quote has included the possibility of insulating the roof as part of that, by laying insulation on top of the roof, but we're wondering whether it might be better/cheaper to do it from within by taking ceilings down. thanks

Answer 1

A flat roof has to be done from the out side of the house, i don't think i quit understand what you mean. Is it going to be a rubber roof? We own a roofing business and that is what hubby is doing today a flat roof (rubber roof). It consist of repairing or replacing the plywood and gluing down rubber to protect the plywood..

here is what a flat roof looks like once completed.and it is very very expensive..
http://www.flatroofsolutions.eu/

some times it is cheaper to have a pitched roof build on..
the car lot hubby is doing to day is a small maybe 5 car garage and is running about $13.000 material and all..the main building cost $85.000 to put a flat roof on...

Answer 2

Insulating A Flat Roof

Answer 3

I'm a bit confused here Andy. If the flat roof needs replacing, when it is removed what is revealed is going to be exactly what you would see if you removed the ceilings. So why consider removing the ceilings if they are ok? When the flat roof is replaced put the insulation in then. Whilst rockwool would have been the material to use there is now roofing insulation board that is much more efficient, 50mm board gives equivalent insulation of something like 150mm rockwool. If the flatroof isn't fitted with suitable vents to keep it ventilated fit them when the roof is done too. The only reason I can see for replacing the ceiling plasterboard is if it hasn't got a vapor barrier ie foil backed board.

Answer 4

Either works I am told, even grass can be used on top of the roof. One thing though if the roof is covered by insulation you may not spot faults early, it will cost more for a re-roof because you'll need the insulation removed and replaced. If you can face the aggravation I'd be inclined to take the ceilings down and do it from underneath.

Answer 5

I think it's down to you and how much faffing you can tolerate. Getting the two jobs done at the same time would save you a lot of disruption and should actually be more cost effective if you're having the roof replaced (removed and re-fitted).

I'd get a quote from another company for fitting the insulation from below (plus an idea of how long the work would take) and then you can actually make a true comparison between the two options.

If you have the skills, you could do the insulating yourself. This would save you money again ..... so long as you wouldn't have to take time off to do the work.

If your time is valuable (financially or socially), then I would opt to get the work done by the same contractor in one go!

Answer 6

You need to be very carefull about insulating a roof from the inside. If you do not install a high quality vapour barrier between the insulation and your room, you will allow moist air to condense in the roof structure (timbers?) resulting in rot and decay. you will aslo get staining on the ceiling from condensate dripping. This all happens because you insulate the roof structure from the warmth of your house and it becomes a cold body that often reaches 'dew point' temperatures (temp at which moisture will condense on the structure).

By insulating on the top of the roof, you keep the structure 'warm', thus preventing condensation and decay.

As vapour barriers are notoriously difficult to install and get an effective seal, I would personally always opt for insulation on the outside face of the flat roof.

Good luck

Answer 7

I have to agree with the first two, It would be better to Insulate from inside, of course that depends on what you have in the house? You may not choose to remove something that you realy like. At the same time as you are reroofing I would give some serious thought on installing a hip roof in place of the flat roof, your insulation will breath much better and give you a neatter looking house. Good luck on whatever you do.

Answer 8

I also would suggest the insulation to be added from underneath, for all kinds of reasons, some mentioned above, mainly later maintenance.
But WHY insulate the flat roof....?.....unless you have a living area underneath, and not just a garage. The whole expense and pain in the proverbial only make sense if you then also insulate the walls well (and garage door) to arrive to a cosy workshop/garage.
If a flat roof is done PROPERLY then it can last maintenance-free for 10 years, without "insulation". Mine did, until recently.....

Answer 9

you can do it both ways but if the roof is being done any way it would work cheaper to have it done at the same time out side,to do it inside you will need to pull done you Celine and will cost more money ( if it was just insulating then it would be cheaper inside but if roof is being done then have it done out side then)
if you have a warm room under that roof ( kitchen bathroom )
then you will need 3 layers 1st being a vapour barrier or the roof will bubble in a short period of time 2ND under coat then 3rd a finish coat stone chippings or green mineral

Answer 10

Good question and I do not know the answers. For the fire issue, call your local fire department and chat them up. Then call your building inspector and talk with him. If he's been around awhile he may have seen it done before and have some information on how it has worked out or what are must do's.