What insulation types are best for a victorian terraced house with an air source heat pump.

[TBreezy]

Hello all,

Trying to work out the best insulation for a Victorian terrace with and air source heat pump being put in. I need three recommendations:

1) what's the best insulation for the external walls (insulating on the inside) and application method - it's solid brick walls.

2) what's the best insulation for the suspended floors?

3) we have original coving in two rooms we want to preserve. We are looking for the thinnest insulation possible to replace plaster. Looked at aero gel but wondering if anyone had experience?

 

[erikwoolf]

We just finished insulating our property. We also have a heatpump. We went for 60mm woodfibre and lime plastering for the walls. Cutting woodfibre is easy using the right tools, I found circular saw to be the best.
For the suspended floor we used hemp/jute. Really nice material to work with. Insulating the suspended floor seemed to make a lot of difference to our comfort levels during winter.
We bought a roll of aerogel (1cm) and used it throughout when there was little space like between the staircase and the wall and to insulate around the coving. It easy to cut but it creates a lot of 'particle' dust so I would definitely advise to do the cutting outside.
What kind of heatpump are you planning to install?

 

[TBreezy]

Were going with a Mitsubishi Ecodan 8.5 & 250L HWC. That and a vent axia B+ sentinel for MVHR.

Makes sense on the aerogel - will get a roll for behind pipework etc. planning on trying to get it up between joists and wall where there is no room for other insulation.

Assuming wood fibre is breathable and you just dab and dot it onto walls?

 

[a twig]

You might find this thread useful:

Plastering question

Hello all, After nearly a year of serious unanticipated structural work we've now finished and can get on with fitting windows, plastering and everything else that we thought we'd be finished by now. I have a question regarding use of wood wool boards on an external facing brick wall. This...

www.periodproperty.co.uk

Covers the use of wood wool and wood fibre as IWI

 

[jamest]

I looked into insulating plasters a couple of years ago, but the technique of application was something I wasn't willing to try myself for fear of cocking the whole thing up and given the price of these products, a cock up could be costly. You need to apply so that there are little voids in the plaster (that's where the insulating effect comes from), but this requires a certain technique, which if not used properly could significantly reduce the insulating effect and so defeat the whole purpose of the exercise. Cork or wood fibre board systems are much easier (and a bit cheaper, than diathonite certainly). The Bauwer plaster may be easier to apply, but seems to have disappeared - their website no longer works!

 

[aockenden]

I looked into insulating plasters a couple of years ago, but the technique of application was something I wasn't willing to try myself for fear of cocking the whole thing up and given the price of these products, a cock up could be costly. You need to apply so that there are little voids in the plaster (that's where the insulating effect comes from), but this requires a certain technique, which if not used properly could significantly reduce the insulating effect and so defeat the whole purpose of the exercise. Cork or wood fibre board systems are much easier (and a bit cheaper, than diathonite certainly). The Bauwer plaster may be easier to apply, but seems to have disappeared - their website no longer works!

Ok, I'll give an alternative perspective on this:

When it comes to insulating plasters, the insulating effect comes from the insulating aggregates which are mixed into the binder (lime or clay typically). It is within those aggregates that air-pockets are formed (which incidentally is what makes those aggregate materials insulating in the first place!). Having some additional air-pockets within the final applied plaster structure, created via some special application method of the plaster (often a pressurized render-sprayer or whatnot) may improve the insulation value further but is not necessary to achieve an insulating effect.

 

[jamest]

You're right, of course. That must be true, to a degree. However, the aggregate grains are really very small and so the opportunity for significant air pockets is limited unless the aggregate grains are dense within the binder and there is plenty of 'overlap' to avoid cold bridging through the binder. My guess would be that adding hemp shiv or the like into the binder is going to have an even more limited effect. The figures quoted for plasters that rely on aggregates or shiv for their insulating effects aren't great - you'd be better off using thin cork or wood fibre board. The plasters that rely on interstitial voids achieved using (in part) the application methods I mentioned earlier, can give much better insulation (so they claim). But aggregate-based insulating plasters are certainly a lot better than nothing at all, especially of you're happy to slap on a 6 cm thickness or even more. Still, I think I'd rather make boards out of the insulating material and use those than chop it up into small pieces and add it to the binder.

 

[aockenden]

You're right, of course. That must be true, to a degree. However, the aggregate grains are really very small and so the opportunity for significant air pockets is limited unless the aggregate grains are dense within the binder and there is plenty of 'overlap' to avoid cold bridging through the binder. My guess would be that adding hemp shiv or the like into the binder is going to have an even more limited effect. The figures quoted for plasters that rely on aggregates or shiv for their insulating effects aren't great - you'd be better off using thin cork or wood fibre board. The plasters that rely on interstitial voids achieved using (in part) the application methods I mentioned earlier, can give much better insulation (so they claim). But aggregate-based insulating plasters are certainly a lot better than nothing at all, especially of you're happy to slap on a 6 cm thickness or even more. Still, I think I'd rather make boards out of the insulating material and use those than chop it up into small pieces and add it to the binder.

Yes I think the reason to use these insulating plasters instead of boards is when you want to maintain the organic curvature of the walls. As for aggregate sizes re. thermal efficiency: when we've been making and applying our own insulating lime plasters, we deliberately use chunky (up to 1 cm diameter) aggregates (coarsely granulated cork, and very coarse hemp shivs) for the first insulating "scratch coat" to maintain as much airspace within the aggregates as possible. We only move to the finer aggregates (perlite and fineer hemp-shiv) for the second insulating coat "float coat".

We've been seeing about a 1 - 2 degree improvement in wall temps (relative to bare stone) for every 2 cm of insulating lime plaster we apply. We are building up to a total thickness of 3 - 5 cm (depending on the location) so hoping for a total improvement of 2 - 4 degrees in wall temps. Plus the walls FEEL much warmer to the touch than the bare stone, like significantly more than just 2 - 4 degrees.

 

[jamest]

Very sensible approach you've taken there making your own with large lumps of aggregate and your temperature figures look pretty good. I don't know if the OP is willing to take your approach though. You've got stone walls, right? I can see that using a plaster rather than boards will help keep the natural look of the wall beneath, plus stone is often not flat anyway, so would need to be flattened before applying the boards. Not so important with the brick the OP has. In his/her case, I'd go with boards (not dot and dabbed though).

 

[aockenden]

Very sensible approach you've taken there making your own with large lumps of aggregate and your temperature figures look pretty good. I don't know if the OP is willing to take your approach though. You've got stone walls, right? I can see that using a plaster rather than boards will help keep the natural look of the wall beneath, plus stone is often not flat anyway, so would need to be flattened before applying the boards. Not so important with the brick the OP has. In his/her case, I'd go with boards (not dot and dabbed though).

Yes ours are curvy stone walls and we wanted to maintain that. Yeah agreed, for flat and straight brick walls it's probably easier (and possibly more insulative per unit of thickness) to go with a breathable board-based approach. There's still the question of which would be cheaper, but I haven't run the numbers so I can't make any claims on that.

If it were me I would definitely be coating the backside of the breathable insulation boards with a layer of lime putty or even clay (like buttering toast) before installing them, to ensure a contiguous, moisture-wicking direct contact between the cold brick and the insulation board. That will ensure that there's little or no room for condensation to form and any moisture that does condense into a liquid on the cold bricks is quickly wicked-away into the capillary structure of the lime / clay "butter" layer, and then into the insulation board, and then into the plaster skim, to then be evaporated back out into the internal atmosphere as water vapour.

 

[a twig]

Part of the reason DIY people get excited about the insulating plaster is actually very little to do with its insulating effects and more to do with the thicknesses you can apply in one pass.

When buying pre-mixed it is classed as an insulation product so attracts 0% VAT. If you have wonky walls and so are needing a significant thickness of plaster to flatten them out the insulating plasters can often achieve that flattening in one layer of insulating plaster, and then just need a finishing coat to get a nice surface, rather than the traditional 3 coat method.

This can work out cheaper and also require less time/effort - at least that was the case when I used a premixed NHL based hemp insulating plaster from Ty Mawr a few years ago, material cost was lower as I needed significantly fewer bags, and I did a whole bedroom in 3 days