Need thinner insulation boards, but can it be done.

[DB9]

Currently doing a garage conversion on a house that I recently bought. Using Celotex with a thickness of 75mm for the floor and walls won't be a problem. However have had the building regs round today and they are stating that for the roof we need to have a 50mm ventilation gap and then 125mm thick ventilation board, this is a problem!

The joists are 100mm and thats all I want to play with for both ventilation and insulation, the reason being is because there will be little head room left if we have to come down 175mm (already rasing the floor by 150mm to make it level with others).

So my question, is there anything out there with an equivalent U value to a 125mm Celotex board but available in 50mm?

Thanks

 

[chappers]

see if you BCO will let you wedge 50mm celotex and then fit tri-iso 10 underneath but you will still lose 35 mm or wedge fit 50mm and then 60mm under

 

[DB9]

see if you BCO will let you wedge 50mm celotex and then fit tri-iso 10 underneath but you will still lose 35 mm

Thanks for the suggestion, losing 35mm is better than losing 75mm.

or wedge fit 50mm and then 60mm under

Sorry not sure what you mean by this.

 

[DB9]

Would you know what U value the Building Regs are after for the flat roof?

Saves me waiting to call her in the morning and can do the research tonight.

 

[mikric]

If your b regs application is after 1st Oct 2010 you need 0.18Wm2k if before then 0.2Wm2k
As mentioned before will they let you fit insulation tight to underside of flat roof, ie no void no need to ventilate.

 

[^woody^]

Full fill the roof void so that there are no air gaps and fit a vapour check to the ceiling. Then you don't need ventilation

 

[geraint]

Full fill the roof void so that there are no air gaps and fit a vapour check to the ceiling. Then you don't need ventilation

... and guess the next question....

 

[DB9]

see if you BCO will let you wedge 50mm celotex and then fit tri-iso 10 underneath but you will still lose 35 mm or wedge fit 50mm and then 60mm under

Chappers, spoke to the BCO again today, was told Tri-ISO can't be used. However they did come up with another solution:

50mm ventilation, 50mm celotex, Thinsulex

I will still lose about 30mm more than I want to but its better 75mm.

 

[^woody^]

But its not better than losing none and having 100mm celotex

 

[DB9]

Full fill the roof void so that there are no air gaps and fit a vapour check to the ceiling. Then you don't need ventilation

But its not better than losing none and having 100mm celotex

I have no idea what you mean here, could you please explain on how this is achieved.

Will the 100mm Celotex give the correct u value that the building regs require?

 

[DB9]

Full fill the roof void so that there are no air gaps and fit a vapour check to the ceiling. Then you don't need ventilation

But its not better than losing none and having 100mm celotex

I have no idea what you mean here, could you please explain on how this is achieved.

Will the 100mm Celotex give the correct u value that the building regs require?