Retrofit Party Wall Insulation

[MikeGrahamT21]

After many years of contemplation about retrofitting party wall insulation between ours and next doors bungalow, I've decided to start getting the wheels in motion, went round to see if he would be OK with us having it done, and got a thumbs up, as long as it doesn't cost him anything, which is fine by me. I've been in touch with Aran Energy Services, and they are getting some paperwork in order (with it being party wall) for him to sign (i've asked them to put that no costs be charged to him), and then a survey in the coming weeks.

 

Hoping everything goes to plan and he doesn't change his mind, as this could save us a good amount on heating, for around £3-400 outlay.

 

Has anyone else had this type retrofit completed? Its more attractive now, since its officially recognised, and you can get ECO funding for it, but still not widely done, due to 2 households having to agree.

Edited May 22, 2018 by MikeGrahamT21

[ProDave]

Unless your neighbour habitually keeps his house very cold, I can't see a great deal of saving from party wall insulation. What am I missing?

 

Now soundproofing benefit, that is a lot more likely.

[MikeGrahamT21]

Leeds Met did some research on it years ago, they also assumed party wall was a 0 uvalue element, but then found out that its actually a very high heat loss component, due to what they now call the party wall bypass effect, blocks on both sides heat up, warm the air in the cavity, and because its not sealed, it rises, and draws in cold air, continually cooling the blocks down, and hence you get massive heat loss.

 

You also see on the roof tiles, above this cavity, any frost/snow always melts there first.

 

I put my hand inside the cavity this February, and my word the amount of heat in there is slightly insane!

Edited May 22, 2018 by MikeGrahamT21

[ADLIan]

Work done by Leeds Met Uni and mineral wool manufacturers association. This is one reason party wall thermal bypass was included in the Regs a couple of updates ago.

 

In theory reduces U-value of party wall from 0.5 to zero W/m²K. Check energy savings - payback at above costs may be long time!

[A_L]

41 minutes ago, MikeGrahamT21 said:

Leeds Met did some research on it years ago, they also assumed party wall was a 0 uvalue element, but then found out that its actually a very high heat loss component, due to what they now call the party wall bypass effect, blocks on both sides heat up, warm the air in the cavity, and because its not sealed, it rises, and draws in cold air, continually cooling the blocks down, and hence you get massive heat loss.

 

Would sealing the top and bottom of the cavity not be sufficient? Assumes sides are already sealed by CWI?

[Mr Punter]

If you are having stuff blown in, you could just do the bottom bit.  Is the cavity open at the top?  Normally it would be closed.  I would not bother.

[ADLIan]

Sealing the edges alone (must be top, bottom & sides and prevent any air infiltration so cavity stop sock) reduces U-value to 0.2 W/m2K. Not sure how you do this in retrofit.

 

Remember injected insulation must be the fluffy stuff (glass or stone wool, min 18 kg/m3) as this has been shown not to adversely impact the acoustic insulation across the party wall. Do not use eps bead or pur as these may (will?) ruin the acoustic performance and neighbours may complain.

[ProDave]

1 hour ago, ADLIan said:

Sealing the edges alone (must be top, bottom & sides and prevent any air infiltration so cavity stop sock) reduces U-value to 0.2 W/m2K. Not sure how you do this in retrofit.

 

So are you saying a well sealed party wall will lose more heat than any of the external walls of my detached house?

 

I'll stick to detached then.

[MikeGrahamT21]

Sealing would be almost impossible retrofit. Yes definitely would only use the fluffy stuff on this, we had one firm trying to do eps, but it would be horrid for sound transmission.

 

expected outlay is around £300, they quote £90 a year saving, but that’s way out. Going to see if we can get any funding for it.

 

so you reckon it’s not worth it then? It’s always hard to gauge how much these type things will make a difference, if it’s cheap enough though and won’t cause any upheaval inside the house then I’ll take a punt on it, at least we will have insulation all round then as a complete solution 

[CC45]

We have added sound insulation onto a party wall - def worth it from a sound perspective.  Cant tell about heat loss. £300 isnt a lot really....

[MikeGrahamT21]

I’m not too bothered about the acoustic, though that’s only because we make the most noise lol. If we are quiet we can often hear phone conversations. But it’s another added benefit. I’ll see how much they want, the £300 quote was from 2 years ago, can’t imagine it being that much more now, and if it’s funded all the better, it certainly won’t harm the building it can only improve it. We also have a few nasty cold spots on the party wall which I am positive this will sort. If the guy changes his mind the only the only other option will be IWI and that will be expensive and probably not as effective, plus we’ll lose thermal mass which currently keeps us nice and cool in the summer 

[MikeGrahamT21]

So getting someone to actually install this stuff is almost impossible, so I've been having a think. We have a single large wall onto the party wall (master bedroom) which I am going to be renovating potentially next year. What effect would knocking all of the plaster off of that one wall, parge coat and then some insulated plasterboard? I'm assuming that would pretty much negate the effects of the party wall bypass?