Loft conversion roof insulation question.

[jaythegorilla]

Hello

I am currently gathering quotes for work on a loft conversion on a 1930s detached house. The roof requires a complete strip and recover with new roof tiles, battens, membrane etc including the construction of dormers.

Whilst the roof is completely stripped is it benefical to have insulation fitted before the new battens, tiles are fitted? Is this known as a warm deck? Or is it better to have the insulation fitted between the doubled-up rafters?

I realise that BC will require the correct U value achieved, just wondering best way to do this. Any saving on head height would be an advantage.

Many thanks for any comments

 

[freddiemercurystwin]

Its very rare to have the insulation on the outside, you would also (technically) require planning permission as you would be raising the roof (albeit by only 100mm or so). There are also likely to be some issues to overcome at the eaves/verges etc where existing gutters/fascias need to be considered. Realistically you only have about 50mm of insulation beneath the rafters anyway although that really depends on the size of your existing/new rafters. It would be a warm roof is you went that route.

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• freddiemercurystwin
• 14 Apr 2010
• 12

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• freddiemercurystwin
• 25 Apr 2010
• 24

 

[DevilDamo]

To achieve the current u-value's, you would be looking at min. 150mm rafters with 100mm (Celotex) insulation between (thus leaving a 50mm air gap) and 52.5mm (Celotex) insulation below the rafters and to have taped joints as VCL and air leakage barrier and lightweight plaster skim.

There are other options but that is one where you can't raise the roof, without having to consult planning... as FMT quite rightly pointed out.

 

[freddiemercurystwin]

thus leaving a 50mm air gap

25mm gap if breathable membrane is chosen.

 

[DevilDamo]

Yup, which I never use/specify as when I used to work at BC, there used to be problems with the breathable membrane.

 

[freddiemercurystwin]

Yup, which I never use/specify as when I used to work at BC, there used to be problems with the breathable membrane.

Come on get with the times DD!

 

[jaythegorilla]

Thanks for the quick replies, really useful. Just to double check, the U value for pitched roofs needs to be below 0.3?

Cheerss

 

[freddiemercurystwin]

Thanks for the quick replies, really useful. Just to double check, the U value for pitched roofs needs to be below 0.3?

No 0.20 or less.

Page 22 of the Approved Document http://www.planningportal.gov.uk/Pp...ortal.gov.uk/uploads/br/BR_PDF_ADL1B_2006.pdf Table 4 Column B

 

[jaythegorilla]

Cheers freddy twin.

 

[deina]

Hi

why don't you give the guys at www.ukhomeextension.co.uk a call they are very nice and good and give you a very quick and cheap quote compared to other builders in London. You phone and arrange an appointment and he looks at the building giving you a detailed plan of the work needed including finances. Stress free. From start to finish. Good luck!

 

[DevilDamo]

The OP lives in Sheffield... why suggest somewhere in London?

First impressions are everything and their website is appauling.

 

[freddiemercurystwin]

Yes a website with no landline or address is always a safe bet!

 

[deina]

What do you mean by apalling? Good or bad?
You should try sheffield definitely because you want it finished in time. Good luck!

 

[freddiemercurystwin]

What do you mean by apalling? Good or bad?

Bad of course!
BTW to both of you, please spell appalling correctly!

 

[deina]

Hey thanks for correction; that is what happens when you are in a hurry.

I know the website has been done by the builder's son, which is only 16 so I congratulate him for saving money for the dad. This company is a small unit, that is why I recommended them as they have all the interest to get jobs done and to do them properly.
What I liked about them is the fact that they take you through the whole project and they do it the way you like it. Nice people and good value for money. Bigger companies take your money and don't care much because you are a number only for them, they have people who come today and you don't see them tomorrow. That was not the case with this company. Builders were the same from start to finish.