Replacing existing internal insulation

Alun · 26-02-2015 6:18pm #1

We live in a semi-detached bungalow built in 1995, and have been looking at options regarding improving the insulation. One of our neighbours has just had the front wall of the house, the only one to have a cavity filled with bead insulation and she's very pleased with it, so we may well get that done, as well as beefing up the attic insulation too.

Now, the side and rear walls appear to be of single block construction, with 2x2 battens attached, filled with yellow fibreglass then a polythene sheet and plasterboard on top of that.

So my question is would there be any merit in replacing this with something more modern with better insulation properties, or would the gains not be worth it in terms of both cost and the hassle involved?

650gs · 26-02-2015 11:53pm

100% even a 50mm insulated board would be better than that go for 90mm boards if I were you not really a big job

Sleeper12 · 27-02-2015 12:09am

filling the cavities is the least effective form of insulation. Use installation boards on this wall too.

Calahonda52 · 27-02-2015 12:33am

Alun wrote: »

We live in a semi-detached bungalow built in 1995, and have been looking at options regarding improving the insulation. One of our neighbours has just had the front wall of the house, the only one to have a cavity filled with bead insulation and she's very pleased with it, so we may well get that done, as well as beefing up the attic insulation too.

Now, the side and rear walls appear to be of single block construction, with 2x2 battens attached, filled with yellow fibreglass then a polythene sheet and plasterboard on top of that.

So my question is would there be any merit in replacing this with something more modern with better insulation properties, or would the gains not be worth it in terms of both cost and the hassle involved?

The math here is easy enough in concept, if you half the heat loss by increasing the insulation at a cost of X, what will be payback period be.
Its a tough one to value but has huge feel good factors attached

My guess re you neighbour is that the front wall is brick clad?

Airtightness I would look at: are the wall vents sealed to the outside of the plaster board or are the holes just punch ed in the wall.

Take one off the inside and have a look see.
If you do take off the existing, whats the storey with running cables to sockets etc?

Alun · 27-02-2015 11:23am

Calahonda52 wrote: »

My guess re you neighbour is that the front wall is brick clad?

Correct, in fact they're the other half of my semi-d. It's effectively the same construction as the side and rear walls but with a layer of brick with a cavity (haven't measured how big) between the brick and the block.

Airtightness I would look at: are the wall vents sealed to the outside of the plaster board or are the holes just punch ed in the wall.

The vents are a bit of a mess to be honest. As you say there's a rectangular hole in the block that lines up with the external vent, but then just a circular hole in the plasterboard that in most cases doesn't even correctly line up with the vent. In fact in the en-suite it doesn't really line up at all. There's no sealing around the room side of the vent, so I'm guessing cold air is just falling down into the fibreglass between the block and the plasterboard.

In the case of the front wall, there's nothing there either, so again cold air falling into the cavity, except in our neighbour's case they discovered when they took the internal vent off that they were faced with a solid block .. the builders hadn't actually put a vent in at all!

If you do take off the existing, whats the storey with running cables to sockets etc?

Good question. Cables to the sockets at least seem to be running down in between the plasterboard and block.

Calahonda52 · 27-02-2015 1:27pm

My guess is that the front wall construction is 4" hollow, clad with brick creating the cavity.

My guess is the side and back walls are 9" cavity block

Take off the wall vent a nd check if u don't mind

Based on what you describe, which is exactly what I expected, the existing insulation is pretty useless.
The 2" battens are not as bad as when plasterboard is dabbed.

The battens should be continuous along the ground and ceiling to form a firebreak so if this is done properly then the air flow through house may be limited enough.

Decide what the plan is before u seal the vent holes to the plaster board as one solution is to put solid ducting from the outer vent all the way in and the gap in wall around the duct made airtight, typically needs to be taped to wall, expanded foam won't do on its own.
You could consider changing the side wall vents to circular vents like are used on EWI projects and then the duct will go all they way in.
Get back to me by PM if u need anything in particular

dathi · 27-02-2015 3:23pm

Calahonda52 wrote: »

The math here is easy enough in concept, if you double the U value of the insulation at a cost of X, what will be payback period be.?

you are mixing your values up here. u value is the value given to in this case the whole wall construction ie. plasterboard battens insulation blocks render.not to the insulation on its own this is the k value. but either way if you doubled either of these values you would lose more heat not less.

BryanF · 28-02-2015 7:38am

Sleeper12 wrote: »

filling the cavities is the least effective form of insulation. .

Could you elobrate in this? Unless you mean cavity block (breeze blocks) it's a rubbish statement.
I would suggest pumping the cavity achieves better insulation continuity than dry-lining, has a better due-point location, retaining blockwork internally means better for fixing things, and thermal mass means the house stays cooler in summer and once warm holds its heat better in winter.

Sleeper12 · 28-02-2015 10:18am

BryanF wrote: »

Could you elobrate in this? Unless you mean cavity block (breeze blocks) it's a rubbish statement.
I would suggest pumping the cavity achieves better insulation continuity than dry-lining, has a better due-point location, retaining blockwork internally means better for fixing things, and thermal mass means the house stays cooler in summer and once warm holds its heat better in winter.

Anyone that has done the SEI training courses on home insulation will tell you that SEI rates the effectiveness of wall insulation From most effective to least effective. Most effective is outer insulation (outside of outside walls) then comes interior insulation (obviously the effectiveness of this depends on the thickness of the insulation). They rate filling the cavities is the least effective form of insulation.

Calahonda52 · 28-02-2015 1:31pm

BryanF: other than the rubbish bit, the points you make are valid, as are the ones Sleeper12.

As regards retro cavity filling, I have zero faith in the process for reasons I have already stated on this forum.
They include no quality assurance on the actual products used as well as issues around the density and completeness of fill.

As to fixing insulation in the cavity during a new build, my opinion is that it is just too difficult to get right and impossible to verify afterwards.

This is based on site experience from 1972

All building processes have their pros and cons and degrees of difficulty to get right on a repeatable, consistent and cost effective basis.

For me, there are better options than cavity fill when measured against these criteria.

Replacing existing internal insulation

Comments