Building Regs, Insulation 270mm??????

[fordyjohn]

Every web site I read on loft insulation states current building regulations recommend 270mm insulation

Can I find in the actual building regulations documents that says this, NO I CANNOT.

Please can somebody please, please tell me what part, chapter, sub section it is.

Thanks in advance

 

[mointainwalker]

Every web site I read on loft insulation states current building regulations recommend 270mm insulation

If you are talking about existing property then the government -or a quango - recommends 270 mm, but adding insulation on its own has nothing to do with BR.

For new-build there is , AFAIK, a whole-house target so it would make no sense to specify for one particular area.

 

[fordyjohn]

Ok, so when asked the question how thick should loft insulation be, what is the answer and who recommends, determines, sets that thickness.

Surely their must be a BR that stipulates such a thing especially as BR's stipulate so many other building stuff.

Also so many websites quote "current building regulations recommend 270mm insulation"

Confused I am!

 

[tony1851]

You won't find this in any regulation because the Building Regulations are usually written as' performance specifications'. In this particular case, the rules simply give standards of maximum heat loss for such things as walls, floors, roofs etc.
In the case of a traditional roof where insulation is put on top of the ceiling, the standard of insulation required is 0.16 watts per sq. m. per 1 degree temperature difference, (if you get my drift!). How and with what insulation material you achieve this is up to you, but for glass wool it is about 270mm. There are other materials which are more efficient than glass wool and which can be used in lesser thicknesses.
Google in AD L1b for the advisory document; the standard quoted above is on page 17, but you won't find any references to which material to use.
In the old days, it was much simpler; they would tell you what to use!

 

[fordyjohn]

Ahhhhhh, I see, I have got a concrete loft floor / ceiling which is 150mm thick, I wonder if that meets the 0.16 watts per sq. m. per 1 degree temperature difference, (if you get my drift!)

But I have also got the roof insulated to 150mm glass fiber rolls in plastic

 

[tony1851]

The concrete ceiling will give practically no insulation value, save for the fact that it is protected from the chilling effect of the wind by the (largely) static air in the loft.
If you are putting insulation between the rafters, you would need a greater thickness of glass wool than 150mm. The thickness you would need to strictly comply with Building Regs would be impractical (probably around 250mm).The most efficient way to insulate that loft would have been to put slabs of Kingspan or Xtratherm (the yellow stuff with foil both sides) directly on top of the concrete, though that stuff is expensive.

 

[fordyjohn]

Tony,

Thanks, just so i completely understand, are you saying that I could achieve the correct standard but my roof rafters would have to be insulated out to about 250mm

Cheers

 

[tony1851]

In a word: yes.
(The figure of 250mm is approximate and might vary by 10 or 15mm either way but the thickness is of that order. I doubt anyone has bothered to work it out accurately because insulating between the rafters of a traditional roof with a closed ceiling is rarely done).
You are supposed to leave a 50mm airgap above the insulation and below the tiles/felt to ensure adequate air flow and avoid condensation.
As well as needing a substantial depth of timber adding to the rafters, that sort of depth would probably intefere with ventilation at the eaves.
Personally, I would have put some insulation board directly on top of the concrete. In that way, the concrete would act as a 'heat sink' and help to even out temperature fluctuations in the house.

 

[mointainwalker]

Unless there is a specifc reason not to do so, I would put 250/270 mm on the concrete for about 10% of the cost of insulation board.

 

[tony1851]

Unless there is a specifc reason not to do so, I would put 250/270 mm on the concrete for about 10% of the cost of insulation board.

I agree 100% on the cost aspect as this board is v. expensive (that's why there are companies dealing in cheaper seconds). I just wondered if he could then have put a few sheets of chipboard on the top and used the loft as storage.