IWI - the loose ends.

[mh12]

Have been contemplating on a few considerations for the nitty gritty of IWI - the last remaining before the big plunge.

I was thinking what happens to the small external wall space between rooms one above the other. Essentially the wall space under floor board of one room and ceiling of room below.

Do the floor boards adjacent to external walls need to removed in order to fit continuous layer of IWI from room below ? Is there a danger of causing unwanted harmful effects to this space around the floor/ceiling such as condensation issues if it was not insulated?

Now I may be overthinking this one. Say the space around floor/ceiling joists was insulated do the parts of floor/ceiling joists that are slotted into external wall brickwork need to have any treatment applied as there will be cold bridging and possibility of condensation at joist ends? By treatment I mean some sort of bitumen type paint to just at joist ends where they meet external wall to protect the joist timber.

I'm always ready to accept constructive criticism.

 

[fernicarry]

Do the floor boards adjacent to external walls need to removed in order to fit continuous layer of IWI from room below

Ideally yes. One reason is the performance of the insulation. As you get close to the end of the run the performance drops off because heat can radiate through the insulation at an oblique angle and will travel through less than the full thickness. The preferred approach is to carry the insulation well past the edge of the space you are insulating in all directions and/or return into the room in all directions.

Obviously not always achievable in a retrofit where access is restricted and you don't want to damage original fabric. If you don't then you get a colder spot in the corner of the room which is the least desirable spot because of less air circulation. I'll freely admit I don't always achieve this, but if you can you should.

So far as joist ends are concerned you should ensure that there are no gaps that air can circulate into. Warm air leaking from the room could cool and condense in those voids. The room I just did IWI on I parged around the joist ends with lime mortar to exclude air from the pockets so far as possible. The caustic nature of lime also creates a hostile environment for any organisms thinking of setting up home in there.

 

[paulc]

I've insulated some of the upstairs walls here. Insulation was carried down below the floorboards as far as the ceiling below and also extends up in to the loft space by about 75mm (the roof timbers limited how far I could go).
Having monitored temperatures in the rooms that have had IWI against those that haven't, I'm not entirely convinced that it is saving much energy. The temperature drops on the worst of cold days in each room is so close to each other that I can't be sure it was worth the effort. That said, the walls feel warmer to the touch and there doesn't appear to be any condensation forming. So on that point, worth doing it myself - Will probably score a few extra points if I ever need an EPC.