Loft insulation

smartpicture

Hi, I currently have 4 inches of loft insulation and would like to top it up (I think 10 inches is recommended now?). However, I have the loft boarded out, not as a usable room but just to make it easier to store things up there. I don't think 10 inches of insulation will fit in the space below the boards, how is this normally dealt with? I can't be the only person with a boarded out loft!

foreversummer

You will need to take up the boarding and raise the joists so the insulation will fit under.

We took some of our boarding up altogether and left some of it as it was without raising the joists if you see what I mean. Sort of half-way house.

I think there may be some material you can fix across the rafters - saw it in a diy shop but know nothing about it. Might be worth a search on google.

Foreversummer

27col

Compromise. Throw out everything that you have not used for a year. This should save acres of space. Then reduce the boarded area to a minimum just around the access hatch. Then remove most of the boarding and top the rest of the roof area with a decent level of insulation. All this talk of building up the thickness of the joist could cost a fortune to do, and you would still need to remove the joists to do it. I am afraid that loft boarding and thick insulation are mutually incompatible.

economiser

We insulated between the rafters under the tiles (It's an older house without felt under the tiles) to top up the overall insulation which leaves us with the boarded out floor space for storage intact.

missile

The flooring acts as insulation too and I would suggest that with 4" insulation plus floor boards is equivalent to 8" insulation.

27col

missile. I think that you are under a gross misapprehension if you think that a layer of chipboard on a loft floor in any way equates to 4" of fibre glass insulation. Even a 4" deep joist does not provide much insulation, so what a simple 3/4" board would provide would be negligible.You have only to check the r-values listed in various tables of insulation value to realise this. If you could get the equivalence by putting a layer of board down, why would you bother with other insulating materials.
As to insulating under the rafters with spray foam, or solid batts of insulation well ok. Obviously it would provide insulation, and stabilise any loose tiles, but you would be heating the whole volume of the loft. This would be the equivalent of adding the volume of another floor to the house to have to keep warm. None of this heat trapped up in the loft would be of much benefit to the people dwelling in the house.

missile

27col, those in climates much colder than ours e.g. Skandinavia and Canada live quite comfortably in their wooden homes.

27col

Yes, the houses are made of wood and they have a huge thickness of insulation in the walls. Not a few millimeters of chip board. Just look up the specification of Canadian or Scandinavian houses.

mech_2

I think people obsess too much about loft insulation. Four inches plus boarding is fine. It's what I have. I have bog standard fibreglass wool with tongue and groove boarding. The boards must surely help prevent air circulating through and between the insulation and the rest of the loft, so I suspect its benefit is greater than just its own r-value.

The additional insulation mandatory for new builds might be worthwhile as the loft is empty and it's all part of the same job, but when you have to move junk and take up boarding to top up existing insulation I don't think it's cost effective. Most of the benefit is in the first 4 inches of insulation. After that it's a case of diminishing returns. Better/cheaper gains can be made improving other aspects of the house, especially draught proofing. Turning the contents of your loft upside down is just hassle.

missile

:iloveyou: Well said that man.

economiser

I think mech is quite correct. Most of the calculations assume whole house heating. Many of us on limited incomes only partially heat our houses and certainly we never heat the upper floor except maybe half an hour or so before bedtime in really cold weather. I suspect therefore that the benefit of loft insulation is somewhat less than the figures quoted. Having said that we do have a total of 250mm because it was cheap to put in on a DIY basis. Maybe that's how we get away without heating upstairs?