flat roof insulation

Joined
16 Jul 2010
Messages
34
Reaction score
0
Location
Northumberland
Country
United Kingdom
I've now been advised that because of the size of the flat roof needing replacement, building control will require that the roof have additional insulation to meet part L. What do you think would the likely cost be of incorporating a decent insulation layer over an area of 40 sq mtrs?

I've already had quotes for doing the boarding and refelting over the area, but I want to have an idea of the extra costs before I start getting revised quotes, as the process seems to take so long.

Thanks for any help.
 
Sponsored Links
I normally use king span tr26 @120mm .this is the proper insulation for a flat roof if it's a warm roof construction.this board is denser so you can walk on it,expensive @ around £55 per sheet covers 2.88sqm per sheet.you will also need screws at 200mm lengths again expensive so as mentioned at least a £1000 supply then there's fixing
 
If you are repairing a roof instead of renewing, insulation upgrade is not required under Part L.

If you did want to upgrade you can combine whats on there, say 50mm with 70mm to give you a U value of approx .18. Overlaying you can bond the insulation in roofing grade PU adhesive. We pay £18 - £22 M2 for 120mm. Tapered schemes from £40-£60 M2.

If your roof membranes are in good condition, you can put a TFX closed cell insulation straight on top, but it will need ballasting to stop wind uplift, the structure needs to be able to support this.

Once i get into work next Friday i can find you the relevant document to present to Building Control. For now, this may help;

* The Building Regulations Part L, Table 5, states that where technically, functionally and economically feasible, an existing Flat Roof that does not achieve a U Value of 0.35 needs to be upgraded to a U Value of 0.25. It further explains that a reasonable test of economical feasibility is to achieve a simple payback of 15 years or less.

Assuming an existing 36 m2 flat roof with a 100mm fibreglass quilt insulation in the roof void, being upgraded with an extra 100mm of PUR roof insulation. We would expect a saving in heating fuel of approx £33 per annum.

The total saving, based on a simple payback over 15 years would be 15 x 33 = £ 495

The typical cost to upgrade a flat roof of this size with vapour barrier, insulation, and increased fascia, would be £1700.

You can therefore argue a case for this not being financially viable.
 
Sponsored Links
If you are repairing a roof instead of renewing, insulation upgrade is not required under Part L.
The situation is that this flat roof predates my owning the property, is believed to be over 20yrs old, and the boarding is of an unknown (but probably unsuitable) material and has definitely degraded and needs replacing. (my local handyman nearly went through it while walking on it).

Now are you saying that even though I need to replace all this boarding it still counts as repairing rather than renewing?

If you did want to upgrade you can combine whats on there, say 50mm with 70mm to give you a U value of approx .18. Overlaying you can bond the insulation in roofing grade PU adhesive.
Unfortunately what is there is not in a good enough condition to upgrade. Now if I understand you correctly, then it would be possible for me to first fix the roof, and at a later stage have some extra insulation added. Though of course doing it in two stages would cost more than doing both at once.

Once i get into work next Friday i can find you the relevant document to present to Building Control. For now, this may help;
Many thanks, I look forward to seeing it.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Back
Top