Inter-floor insulation

[RogerS]

Suddenly realised this evening that there is potential heat loss via this route.

The joists supporting the upper floor are open at the external wall end and so a potential route for heat loss, I guess ? The heat loss from the ceiling of the room below and heat loss through the flooring of the upper rooms.

But how to fix it? The upstairs floors are chipboard. I could cut a strip out of them, say 15" wide, at the external wall end. Cut Kingspan to fit the rectangle formed by two joists, the ceiling of the floor below and the floor of the upstairs room, foam any gaps then faff about with supporting bits of timber to support the chipboard where the cuts were made and replace the strips.

Or ignore heat loss downwards through the upstairs floor (it will be chipboard and oak with the occasional (thin!) rug)) and board the downstairs ceilings with insulated plasterboard. The ceilings are going to be over boarded to cover the Artex anyway. (side question...how do they know where to put the screws in to hold the plasterboard up?). If so, what thickness insulation ?

Or am I being paranoid and the Law of Diminishing Returns needs applying? Many of the rooms have a large RSJ down the middle and the joists fit pretty snugly into them and so the potential for air movement between the joists and (presumably) carrying the heat away is limited.

Mmmmm..... :eusa-think: as I type this I'm starting to think that I'm being over-fussy.

What does the team think ?

 

[Mike G]

Finding the joists is easy. Knuckle, brad-awl, then tape measure.

As for your insulation......a sketch section would help, but that detail is a classic for heat loss. For a start, I suggest this is a case where mineral wool would be much better suited than Celotex. You can stuff it in properly, and get all the gaps, but Celotex you'll never get close to blocking every avenue of heat loss. If you're overboarding the ceiling anyway, would it be practical to cut say 18 inches away of the existing ceiling around the outside walls of the house? If so, just keep stuffing mineral wool in until you can't fit any more, pack out the joists to the thickness of the old ceiling, and then tack the ceiling in the normal way.

 

[RogerS]

Thanks for the reply, Mike.

The word 'detail' made me smile. When I was discussing what was required on the water tables, the surveyor had written

"Supply and fit new code 4 lead watergate as per detail between low level roof and rear elevation, create upstand to masonry. Raggle and fit code 5 cover flashing dressed down over water gate upstand as per detail."

and we were scratching our heads coming to the conclusion that we were missing the 'detailed' specification or supplementary information. I now realise where we were going wrong :lol:

Back to the inter-floor insulation, I like the idea of coming at it from the ceiling, the major downside as I see it is getting eyes full of plasterboard dust (even with goggles). That and, in my experience, ceiling plasterboard is usually supported around the perimeter of the room and goes up first. This support then tends to get hidden to a greater or lesser extent once the plasterboard on the walls has gone up and so refitting the removed plasterboard patches might prove problematic. I'm tending to favour attacking from the top.

You mention stuffing mineral wool in the whole of the gap between the ceiling joists - if I follow you correctly. Isn't this overkill? Surely any heat loss from the room below is a heat gain for the room above and so that rooms' TRV will switch off that little bit sooner ? I'm all in favour of sealing up the open ends between the ceiling joists at the external wall end.

This whole issue of heat loss/gain between rooms reminded me of my first Excel spreadsheet 30 years ago when I went to excruciating detail to model the rad and pipework sizes for our last house. Even to the extent of starting off with 28mm pipe down to 22m branches down to 15mm branches. I seem to remember even calculating the pressure losses (or whatever they're called) at each 90 degree bend!

The spreadsheet had the ability to dial down the design temperature for each room independently. In the early stages, we were using fan heaters to heat the rooms we were using and I was concerned that our living room needed much more heat than the spreadsheet suggested. Couldn't work it out. Spent ages poring over the spreadsheet. Then I had a and looked at the design temperatures for the adjacent rooms. They were set at the design temperature but unreality many rooms had zero heating. So dialled down the design temperatures to those rooms to something closer to outside temp and bingo....watched the heat requirements of the living room rise to close to what we were pumping in.

Also, as expected, I could never dial down individual room temperatures to outside ambient simply because of heat gain from adjacent rooms!

 

[Mike G]

....You mention stuffing mineral wool in the whole of the gap between the ceiling joists - if I follow you correctly. Isn't this overkill? Surely any heat loss from the room below is a heat gain for the room above and so that rooms' TRV will switch off that little bit sooner ? I'm all in favour of sealing up the open ends between the ceiling joists at the external wall end.........

That's all I meant.......stuff mineral wool in to the full depth of the joists but only for the thickness of the external wall, not over the whole floor area. Essentially just infilling the gap in the external insulated envelope of the building. As an aside, there is sometimes a point to filling a floor void with insulation: sound transfer. A wooden floored bathroom above a dining room, lounge or kitchen, for instance, would be a good case for doing this. However, that's not what I was suggesting for you.