More insulation or more boards?

[mpaxton78]

I am sure this will seem like a daft question to many of you but here goes...

We live in a 1936 semi and the current loft insulation is pathetic at best. The joists are only 75mm thick with insulation at about half this depth, but about half of the space is also boarded with chipboard. I understand compression of insulation is a bad idea, but I have seen it written that the chipboard itself has good insulating properties.

So my question is - how effective is the chipboard flooring in terms of insulation properties - and for the unboarded areas, am I better to "top up" to the 270mm level or board this area too?

 

[JohnD]

Chipboard is nowhere near as good an insulator as... insulation is.

Top up to the full depth of the existing timbers for a start (including under the existing boards)

You can also counter-batten with an addition row of timbers at right-angles to your existing ones, allowing you to add another layer of insulation without it being squashed by the boarding.

By screwing the new timbers to the old ones, this will also stiffen up the ceiling and spread your weight better when you are clambering about up there. However it will not add eneough strength to treat it as a habitable room or store heavy objects. It also enables you to support the chipboad without it crushing cables etc.

It might be possible to put rigid foam on top of the timbers and put your chipboard on top of them, but the boards must be fully supported by having timbers under all joints and not expecting the foam to add any strength.

Parts of the loft that you do not expect ever to walk on can have extra insulation flopped over the timbers. You should not insulate over heavily-loaded cables like Electric Shower or Immersion Heater cables. Lighting circuits are very lightly loaded so you can insulate over then if need be.

 

[mpaxton78]

Hi JohnD,

Thats pretty much what I had thought, although isn't adding more timber on top of relatively thin joists likely to cause more problems rather than providing additional support?

I am all in favour of insulating as best I can but I don't want to create any risks in the process.

Also, you say to fill to the top of the existing joists under the boards but I understood that an air gap was required - is this not so much of an issue given the depth?