Changing insulation

[Lee989]

We've just moved into a 1970's dormer bungalow style house (where there's a large gable roof with the 2nd story and a smallish loft built into the roof). Whilst laying some network cables between rooms, we've found the previous owners had blown-in insulation in the 2nd-floor walls (which are part stud wall and part roof). I imagine that is nowhere near the recommended U value. Some of this has fell down leaving uninsulated areas as well.

After lots of googling, I was thinking of taking down the plasterboard and put PIR between and under rafters. And eventually (£££) replace the old rockwool in the loft with PIR as well so we have a thick thermal blanket all around.

My questions:

1. Do I need to involve BC, or can I just get on with it myself?

2. I know I should be aiming for 150mm of PIR to meet regs, but with a 50mm air gap, plus the plasterboard finish and possibly additional battens, it's not an insignificant reduction in room space. Is there any allowance for older properties under regulations for less insulation or is it suck it up, room space and cost aren't our problem, do what you're told. I know it might cost more per year in heating if I don't have the full amount but presumably, it wasn't significant enough for the previous owners to install better insulation themselves.

 

[robinbanks]

I imagine that is nowhere near the recommended U value

You don't need to imagine, you can calculate it. Imagination is unreliable.

presumably, it wasn't significant enough for the previous owners to install better insulation themselves.

I don't really understand your presumption there. You appear to be labouring under the misapprehension that the previous owners were insulation savvy and carefully calculated exactly how much they should install in order to reduce their heating bill by X. The vast majority of people are utterly ignorant about anything to do with building heat loss, and in any case it's your house now and you should decide what your own appetite is for buying insulation versus paying the gas bill, based on your own appetite for building work, space loss, bill reduction, planet saving etc etc. Blaze your own trail rather than following what you assume to be someone else's?

Do I need to involve BC, or can I just get on with it myself?

You can just get in with upgrading insulation but if you're making significant alterations to thermal elements of a building (changes to shape or openings in walls, roofs etc) hen you need to upgrade insulation in line with regulation

I know I should be aiming for 150mm of PIR to meet regs

It sounds like you're reading the new build spec, the renovation spec isn't so onerous, though personally I'd chase new spec anyway. Consider using wool on difficult areas as it's easier to install around oddly shaped features.. PIR is great but if difficulty installing leaves gaps that cold air can get round its vastly diminished effectiveness. For example I would wool between rafters and board over rather than board and foam between rafters.. Pay attention to fraught detailing too. Insulation is not he be all and end all. Installing 150mm of kingspan everywhere in an house that has draughty old sash windows with single pane glazing is kinda pointless if all your warm air is just going to blow out of a gap. Making a house energy efficient with regards to heating and heat retention is a holistic endeavour, not just insulating bits here and there

 

[Diver Fred]

Making a house energy efficient with regards to heating and heat retention is a holistic endeavour, not just insulating bits here and there

don't forget ventilation is needed to reduce damp as is a change in behaviour - no regular drying/airing on radiators. Older houses with draughrd were easier to keep dry.

 

[robinbanks]

All part of the holistic endeavour I mentioned.. if one is going to that extent the next step is an MVHR

don't forget ventilation is needed to reduce damp as is a change in behaviour

I'd labour the behaviour point over the uncontrolled ventilation point

Older houses with draughrd were easier to keep dry.

But harder to keep warm