Insulating a flat roof

doningtonphil

Hello

Posted on another thread but been told I might have more joy here.

We are buying a bungalow where the rear half of the property is a flat roof- which accounts for all of the kitchen and half of the living room. The Energy Performance Certificate states the flat roof is assumed to be minimally insulated.

As the roof is one of the key routes of heat loss, how do we increase the insulation?

One idea is to create a false ceiling a few inches below the existing and filling the void with fibreglass (also allows us to insert spot lights).

A few questions:
Is this the best solution?
Are there better combinations of insulation than fibreglass?
What about condensation?
Should an air gap be left or the space packed tight with insulation?
Should it be ventilated?
Is any sort of membrane required?

As always, I look forward to any advice anyone can share

Many thanks

vaio

think about insulating on top of the roof.......

less work, no mess, no loss of internal space and it will keep the roof covering away from the weather so extend its life.

doningtonphil

so how does insulating the outside work? Are there specialist contractors and materials?

We don't mind the mess as we are gutting the place anyway (including a rewire which could allow cables to be routed above the false ceiling. The ceilings are high so no worries about losing internal space

I look forward to hearing more about the external solution as well

salesian1

You may be better off waiting until it starts to leak then having a taper put into the new roof. superhomes.org. will give you resources to insulate-a-flat-roof. A warm deck is preferred now. A cold deck is banned in Scotland owing to heat loss. In other words insulate the ceiling rather than the roof. Watch out for ventilation in the 'cold' space. Rotting roof trusses will cost more than the energy saved .

doningtonphil

we are in Scotland.

I saw another article about 'cold decks' being banned but is that insulation under the roof or on top of the roof that is banned?

The roof was recovered (bitumen/felt) in 2006 and appears in good condition. I know it will degrade eventually. Is there insulating work that can be done without stripping the existing roof and ceiling?

JACKHANDYMAN

Hi, If your flat roof is covered with felt, then it would be obvious that this will eventually split and leak in the long term. Personally i would remove the felt and create a cavity using firrings (tapered timber) and attache new marine grade boards. insulating the roof cavity with either fibreglass or polestyrene beforehand. The roof can be covered with fibreglass (grp) that will have a guarantee of over 20 years and will solve your concerns

cte1111

Our flat roof had no insulation when we bought the house. In our bedroom, I had the ceiling replastered so when the builders brought the old ceiling down, they put rolls of insulation in then put the new ceiling on top.

A few years later, the flat roof needed replacing, we then had more insulation put in from the other side. It's made a big difference to our bathroom, where as before we were having problems with mould, it's now fine.

Gloomendoom

salesian1 wrote: »

You may be better off waiting until it starts to leak then having a taper put into the new roof. superhomes.org. will give you resources to insulate-a-flat-roof. A warm deck is preferred now. A cold deck is banned in Scotland owing to heat loss. In other words insulate the ceiling rather than the roof. Watch out for ventilation in the 'cold' space. Rotting roof trusses will cost more than the energy saved .

Isn't this ärse about face?

salesian1

yes whoops!

vaio

doningtonphil wrote: »

so how does insulating the outside work? Are there specialist contractors and materials?.....

The ones I've done involved interlocking sheet material (dow roofmate?) with paving slabs on top to stop it blowing away and gravel to fill in the gaps around the edges.

Used to be called upside down roof and were a standard detail in lots of telephone exchanges, multi layer hot laid asphalt was the waterproof membrane of choice