40mm wood fibre IWI, ground floor only

[TAndrews]

Hi

I'm planning a refurb of our Victorian coach house (solid walls). A couple of the rooms downstairs are very cold in winter since the external walls in those rooms get particularly cold. Hence I'm considering internal insulation - breathable, wood fibre, lime plaster etc. This is more about room comfort as first priority, than saving energy.

My understanding is that ideally (usually?) you would apply IWI to a whole elevation, ground and first floor above. But in my case that would triple the complexity given the configuration/detailing upstairs, and the rooms above are pretty comfortable as they are. I think the risk of doing ground floor only, supposedly, is that moisture is then more focussed on the relatively colder walls in the upstairs room, increasing the condensation risk in that room. (That's my crude understanding but TBH i've not found it articulated very clearly.)

I would hope, however, that going with a modest 40mm of breathable wood fibre downstairs (and up between intermediate floor joists) would mean the risk of this unintended consequence is pretty low.

I'd be interested in any perspectives on this and whether in reality it's very common to insulate on a room-by-room or floor-by-floor basis vs whole elevation all at once.

Many thanks!

 

[fernicarry]

The way I've understood it is that partially insulating means the performance tails off as you get to the end of the insulated section because you have to consider heat loss not just in a straight line outwards but also conduction from the internal walls past the end of the insulation. The lower performing part will be more prone to condensation as it will be cooler whilst the rest of the room is warmer and the air is wetter. This section is also typically in the corner of that room so a bit of a double whammy as there is naturally less air circulation. I don't think it necessarily drives condensation to adjacent rooms but I suppose circulation of warmer air from downstairs to upstairs could make that possible? I think unless you make the insulated room exceedingly air tight too then thats probably not going to be too significant.

The usual way to deal with this is to return the insulation into the room along the internal wall/ceiling/floor. Having a thick lump along part of the internal wall isn't always the most desirable detail though. The advice to do the whole elevation probably stems from the fact that its just simpler that way but even then you need a return onto the uninsulated elevations. It does rather depend on you having the luxury of completely stripping that elevation. If I was starting over I might be thinking along those lines though. I've done a few ad-hoc bits of insulation here and I do feel the benefits but I think to get anywhere near the sort of performance that would bring energy bills back to pre-cost-of-living-crisis levels really needs a bolder approach.

Going up (and down) between the floor joists is a good idea but may not be enough of a return to even out the performance. Parging around the joist ends with lime mortar to completely exclude air from them is also recommended so that any air leaking from the room is unable to condense on them.

Whats the construction of your floor? I have a suspended wooden floor and at the end of last year I stapled a breather membrane below most of it. I have partly insulated between the floor joists too but thats still a WIP. The difference has been quite noticeable already especially with the gales over the last few days so a useful uptick in comfort for not much outlay.

If you search my other posts you will find some links on this subject,.

 

[paulc]

I'm insulating the walls bit by bit here, concentrating my efforts on the upper half as these are solid brick walls. Having done a couple of the ceilings downstairs, I took the opportunity to stuff the space between the joists with fibreglass loft insulation. The thought behind that was to cut down on any draughts blowing around and to reduce noise. Have also filled between the uprights of the internal stud walls. Don't think it has made much difference in cutting down noise transmission.
The few walls I have insulated to date have made a noticeable difference in that the rooms are warmer, no more condensation on the walls, and a nice flat surface to decorate.