Recommendations for mineral wool cavity fill installers

Can anyone recommend a contractor/installer to fill cavities with mineral wool? We’re in the Calder Valley so Lancashire/West Yorkshire border. I’m keen to find someone who will do a quality job.

As far as I’m aware most installers use polymer beads but we’d rather not use oil-based materials where possible.

To me Calder Valley is synonymous with wind driven rain, at least for the autumn and large parts of the winter. Before contemplating CWI of any sort you need to check and if necessary rectify your weatherproofing. I would start of by looking for cracked or spalled stone/brick and the state of the pointing.

Yes, you’re right. We’ve actually got a whole house retrofit plan to get to EnerPHit Plus. One of the first stages of work is to get the cavities filled.

The bungalow is rendered but it’s losing key so that also needs to be replaced at the same time to prevent driving rain reaching the outer layer of brickwork.

Hi, we’re in the calder valley too and also exploring cavity wall insulation options, would be very interested to hear if you find anyone. So far I’ve only had one recommendation of a company who use beads. We are also a bit nervous about the rain conditions as Tim mentioned and we don’t have an external render. We’re a mid terrace so also wondering what effect it would have on our neighbours.

Congratulations on your ambition.
CWI on its own is unlikely to get you to EnerPHit, unless you have unusually large cavities. If you are able to go straight from installing CWI to EWI then you could save the cost of making good the existing render.

Welcome to the forum.
This is often better than leaking render as the bricks can dry out in summer. You do need to check your walls as described above before fitting CWI. You will also need to check whether the outer leaf of the house is part of a continuous cavity along the elevations of the whole terrace. Not having tie-ins at the party walls would give a more weatherproof finish and tampering with that for one house only could give problems for you and your neighbours.

Yeah, I’m aware CWI won’t be enough. From PHPP calculations it’s CWI and then 300 mm wood-fibre insulation, if I remember correctly.

We are planning to do CWI and re-render plus some maintenance and airtightness works this year. PHPP shows CWI alone will save over £700/year at current gas prices. For several reasons, it’s likely to be several years before the EWI goes on, so the render needs to be done to protect the cavities.

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Likewise! I’ll share here if I do.

Looks as though you need tropical style eaves. But than in anticipation of global warming we probably all need those (to shade the walls from the heat of the sun and deflect tropical rains away from the walls/footings.

Thanks Tim. Pretty confident the outer leaf doesn’t have tie-ins at the party walls - brickwork is consistent along the terrace with no identifiable change at party walls. A CWI company had told me they would put a brush type divider to stop the insulation going to the neighbours it would be fed through a hole at the top and out of another hole at the bottom. Do you think that would cause issues?

Another concern of ours was that we are number 2 on the terrace so if we did CWI it would isolate no 1 from the rest of the terrace cavity, could that create problems for them with reduced air movement in the cavity?

Yep, most of our house already has a large overhang. Only one part will need the roof to be extended out to accomodate the EWI.

I can’t comment on your question to Tim but I would tempted to try and get your neighbour(s) in on it too. You might be able to negotiate a good deal with the installer if they do both at the same time.

The ideal would be to get your neighbours to buy in and all have the work done together. That would reduce the price per unit and give you the best result as there would be no thermal bridging at the joins and corners.

I’ve lived in a property that shared the cavity with the maisonette below but it was isolated from my next door neighbour. I did try to get my 3 neighbours to buy in but none were interested. The property below was the big issue, as you can imagine, but the location was not prone to driven rain or high humidity and we were able to install foam. According to the fitter it went down to my neighbour’s lintels, so she would have had a warmer ceiling and I do think we had a warmer floor! That could have been thanks to the foam very much reducing air movement between ceiling and floorboards by blocking any air leaks.

I’ve not heard of the brush type divider and it does seem dubious to me. You have to be sure that it won’t convey any moisture from the outer wall into the cavity or your insulation. You also need a party wall agreement with each of your next door neighbours before doing anything that might affect their properties.

The neighbour at number one will gain by having less air movement in the cavity although the difference will hopefully be minimal. The cavity isn’t meant to be draughty, it is just to stop water that penetrates the outer wall reaching the inner one. Your neighbour on the other side will also gain slightly for the same reason. Any houses further along the terrace won’t be affected.

Number one have the most to gain if they join you, as they have 3 walls to insulate and by you having CWI they will not have any thermal bridges. If necessary you could pay the full individual price to subsidise them a little if they are reluctant. After all, their bill will be more.

I suppose there isn’t any chance of getting either neighbour agreeing to you insulating the first metre of their walls free of charge? That would eliminate your thermal bridges. Preferably insulate across to the nearest window/door or 1 metre elsewhere.

Thanks Tim, that’s really interesting to hear, sounds like we need to have some more chats with the neighbours and hope we can get them on board :crossed_fingers: Wondering if it’s worth getting an independent cavity wall survey to be extra sure that the condition is good enough for it to be filled.

Borrow the Carbon Coop borescope camera. You can then examine the cavity from above, airbricks and existing openings without having to drill. You may decide to drill through a mortar bed in places to see what is in any blind spots and then re mortar. A specialist would probable remove the odd brick to do the same.

You are looking for rubble, snots (dropped mortar from the brick layer(s)) and very importantly, any wood.

Ideally you should see two clean flat brick or block walls running absolutely parallel. But you won’t!

If accumulated debris bridges the damp course this needs immediate remedial action (and tell your neighbours to get theirs checked). Anything else is a matter of judgement and risk. The odd brick that is not quite aligned won’t matter and where mortar has oozed out a little is not a worry either. Timber is another matter. If there are joist ends is there good clearance from the outer leaf? There should be. If there is wood debris, stopping the airflow around it is an absolute no no. The wood will need to be removed first. If any debris fully bridges the cavity it probably ought to be removed as it can act as a bridge for damp and will become a thermal bridge too. However if there is only a little the structure should remain sound.

If you see anything worrying or you don’t understand call in the experts.

Take photos of everything and note where they were taken. They may prove invaluable later.

Thanks Tim, we’ll do that and see what we find.

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