how to best insulate and board this loft space

benson1980

Hi all,

After a bit of advice for our next project. We have a bit of an unorthodox set up in our loft space which essentially is split into two. We have a converted loft room (albeit low head height) which the kids use as a play area, and then the actual loft which we use for storage which is accessed from a doorway from the former. The door and lining had to come off to fit the new unvented cylinder in, so I need to redo all of that as well.

This therefore leaves us with an area where I don't really want to add to the floor height that much, as we would like to keep the play area for the kids, and in the converted bit my plan is to completely refurbish, reboard and reinsulate between the rafters.

Here's a photo of the loft area currently. Evidently the boarding has been done badly with just random offcuts/side panels being used, and the loft insulation is patchy as well. The joists are 100mm thick. I'm not massively interested in the diminishing returns of adding really thick insulation levels and understand that something like a 100mm celotex type insulation therefore may be the best bet if looking at a thinner insulating layer? From a bit of googling it also seems like boarding directly onto the joists isn't the best idea so was thinking of just adding some kind of battening in the opposite direction so perhaps to the same level where it has been built up for the cylinder to sit on, thus allowing air gap over the celotex? Quite what I'd do at the door threshold I haven't quite figured out as it would be a little odd having an immediate step up but that's obviously not a massive issue.

Any advice or other suggestions appreciated.

Herbyme

I can’t help but I’m curious to hear what others suggest. I have a somewhat similar problem, just the one loft, partly boarded, a few ceiling lights sticking through the insulation, which is nowhere deeper than about 100mm and less where electricians have thrown it around to get at cables in the past. The joists are only 100mm deep ie where there is  that amount of insulation, it is sitting at the top of the joists.  

Because our house has a big footprint and our projected monthly bills are now well over £1k, I’m looking at insulating it to the recommended 270mm, I’d like to know if it’s ok to just lay it on top of joists, as long as no one will stand on it? I can do that myself, the bits I can get at, but paying someone to do anything more complicated may not be worth it (I think - but who knows?)

Bendy_House

benson1980 said:

Here's a photo of the loft area currently. Evidently the boarding has been done badly with just random offcuts/side panels being used, and the loft insulation is patchy as well. The joists are 100mm thick. I'm not massively interested in the diminishing returns of adding really thick insulation levels and understand that something like a 100mm celotex type insulation therefore may be the best bet if looking at a thinner insulating layer? From a bit of googling it also seems like boarding directly onto the joists isn't the best idea so was thinking of just adding some kind of battening in the opposite direction so perhaps to the same level where it has been built up for the cylinder to sit on, thus allowing air gap over the celotex? Quite what I'd do at the door threshold I haven't quite figured out as it would be a little odd having an immediate step up but that's obviously not a massive issue.

Any advice or other suggestions appreciated.

Hi Benson.

What's under the existing floorboards? And are you planning to lift them?

Anyhoo, pretty sure all I'd do is to pack down into all the inter-joist voids with loft insulation, and replace the boards over them. That should give you a pretty effective 100mm of decent quality insulation, as good, I'd hazard, as - ooh - 200mm of normal loose-laid loft insulation*. Possibly better.

If you want to go to the effort of adding battens to raise that floor to match that of the tank's, then do so, but I doubt you'd detect any improvement. If continuing with loft insulation, then add the battens to run along the tops of the joists so that you now have ~150mm.

* Loose-laid loft insulation almost certainly will have voids and gaps, most notably along the joist-ceiling corners. Cables and protruding light fittings tend to raise it and leave further gaps. Subsequent layers - required to get it up to ~300mm - will again almost certainly have gaps between the rolls, and between the layers - it just doesn't 'sit' that effectively. And finally, the top few inches will be quite well ventilated, so will have relatively little insulating effect.

A good 100mm packed down firmly between the joists, and gently compressed by the boarding above, will not only give a fully-effective 100mm of insulation, but less through-draft (to remove some of the escaping heat), and an additional 20-odd mm of timber insulation.

I suspect there will be little difference between them.

benson1980

Bendy_House said:

benson1980 said:

Here's a photo of the loft area currently. Evidently the boarding has been done badly with just random offcuts/side panels being used, and the loft insulation is patchy as well. The joists are 100mm thick. I'm not massively interested in the diminishing returns of adding really thick insulation levels and understand that something like a 100mm celotex type insulation therefore may be the best bet if looking at a thinner insulating layer? From a bit of googling it also seems like boarding directly onto the joists isn't the best idea so was thinking of just adding some kind of battening in the opposite direction so perhaps to the same level where it has been built up for the cylinder to sit on, thus allowing air gap over the celotex? Quite what I'd do at the door threshold I haven't quite figured out as it would be a little odd having an immediate step up but that's obviously not a massive issue.

Any advice or other suggestions appreciated.

Hi Benson.

What's under the existing floorboards? And are you planning to lift them?

Anyhoo, pretty sure all I'd do is to pack down into all the inter-joist voids with loft insulation, and replace the boards over them. That should give you a pretty effective 100mm of decent quality insulation, as good, I'd hazard, as - ooh - 200mm of normal loose-laid loft insulation*. Possibly better.

If you want to go to the effort of adding battens to raise that floor to match that of the tank's, then do so, but I doubt you'd detect any improvement. If continuing with loft insulation, then add the battens to run along the tops of the joists so that you now have ~150mm.

* Loose-laid loft insulation almost certainly will have voids and gaps, most notably along the joist-ceiling corners. Cables and protruding light fittings tend to raise it and leave further gaps. Subsequent layers - required to get it up to ~300mm - will again almost certainly have gaps between the rolls, and between the layers - it just doesn't 'sit' that effectively. And finally, the top few inches will be quite well ventilated, so will have relatively little insulating effect.

A good 100mm packed down firmly between the joists, and gently compressed by the boarding above, will not only give a fully-effective 100mm of insulation, but less through-draft (to remove some of the escaping heat), and an additional 20-odd mm of timber insulation.

I suspect there will be little difference between them.

Thanks BH- funnily enough this is exactly what I've opted to do and loft boards delivered today. Keep it simple....and far cheaper. 

Not planning to lift the floorboards in the playroom bit but that part needs replastering/velux windows relacing and full refurb so will just make sure between the rafters is properly insulated.