1980s house - improving insulation

[guitarsammy]

I live in a 1985 Barratt house in Northern England, a 4-bedroom detached property in an exposed location. Despite having relatively new double glazing, ample loft insulation, and previously insulated cavity walls, I am looking to enhance warmth and reduce gas consumption. Through my basic thermal camera survey, I've pinpointed key areas for improvement:

 

• Downstairs is noticeably colder than upstairs, attributed in part to the uninsulated floors over a ventilated cavity.
• External walls exhibit a 'hollow' sound upon knocking, presumably due to plasterboard with a cavity between it and the blockwork. However, certain spots, particularly around windows like lintels, act as cold bridges.

 

Considering the long-term nature of this project, I have a few questions to kickstart my planning:

 

• Insulating the floors seems potentially expensive and disruptive. Would lifting and insulating beneath the engineered wood flooring/Weyroc be the only viable option, or is there an alternative method?
• Despite having cavity wall insulation, would injecting insulation into the hollow spaces behind the plasterboard on external walls be beneficial by further enhancing u-value? Could this cause condensation issues? Alternatively, is it more practical to remove the plasterboard entirely and replace it with insulated plasterboard to address thermal bridging in those areas where the masonry is solid? 

[ProDave]

It sounds like you have a "plasterboard tent"  The name given dot and dab plasterboard installed badly so the edges are often open to cold areas like under floor, lofts etc that let cold air get in between the walls and the plasterboard, largely negating the insulation in the walls.

 

One of the plasterers will advise but as a minimum you need to seal all the edges of the rooms which will probably be quite destructive.

 

The lack of floor insulation to do it properly means lifting the floor room by room to expose the bare joists and insulate properly before replacing the flooring.

[SteamyTea]

If you are a fairly practical person, consider making an air blower that fits in a suitable window.

Find out where the leaks are, before you squirt anything into unseen cavities.

[Roger440]

Sadly, Dave is probably right. Maybe cut a hole somewhere unobtrusive and see if you can detect any air movement behind the plaster board. Especially if its windy.

 

Steamy suggestion is where to start though. Go for the easy wins first.

 

[Gus Potter]

6 hours ago, guitarsammy said:

I live in a 1985 Barratt house in Northern England

If you have masonry cavity wall construction then is there any potential for external wall insulation (EWI)? Often the gables are a good target area, lots of exposed masonry, less hard detailng around windows. Just check though that the space between the wall and the boundary will still comply with the regs if you added say 110mm of EWI + render etc. Also you need to check the detailing at the eaves and check it's not going to foul any other ventilation slots, say in a soffit for example. EWI can look unobtrusive if executed well, but if not..

 

Next would be the attic, lot's of heat lost here, is there enough insulation and can you get more in? I always like to start on the outside and see if there is a good line of first defense against drafts, is the mastic good round the windows for example. What are any soffit vents doing? .. are they venting say the attic as intended or are they encouraging other drafts and convection currents where they are not supposed to. Get up in the attic and check the eaves venting detail. The concept is that each layer of fabric provides layers of resistance to the air flow.. a bit like adding up the cumulative resistances of layers of insulation /materials to get an over all U value.

 

This is a bit of a technicality but on timber suspended floors you need to have external brick vents at 2.0m centres to align with the NHBC requirements. Link is below.

 

https://nhbc-standards.co.uk/5-substructure-ground-floors-drainage-and-basements/5-2-suspended-ground-floors/5-2-10-damp-proofing-and-ventilation/

 

 You live in a windy spot thus a reasoned argument could be made to reduce the effective area of the ventilators. You could consider / experiment by partially blocking off some of the vents on the predominantly windward side.

 

This would tend to reduce the air flow but as the leeward vents are more open it could reduce the air pressure under the floor which would mitigate drafts forcing themselves up through the floor. Now some folk may have a hairy canary at the thought.. but practically.. when we are doing the insulation calcs for suspended floor insulation we take into account exposure, the solum space and so on as the amount of air flow under the floor impacts on the performance of the insulation.

 

You may want to open up again in the spring.

 

Air tighness is a key, partcularly downstairs. But remember the more air tight the more risk of condensation if not controlled. In some ways you need to rule out the things that are not causing a problem. It could take you a bit of time but well worth being forensic. In the round it's worth thinking, cost wise is it easier / cheeper to add things compared with deconstructing parts and then replacing?