[Help] Property insulation advice please

shingle · Apr 16, 2024

Good morning all

Just posting a question on behalf of my eldest son who has just bought his first house. The property is currently uninsulated and he's trying to decide between cavity wall and 270mm loft insulation. He can only stretch to getting one of them done. He's read some horror stories about cavity wall causing damp issues and so is inclined to go for loft insulation. However, in around 5 years time he is looking to get loft a loft extension and so hes not sure whether loft insulation is a good investment if its the case that loft insulation will ultimatly need to be pulled up and discarded.

Does anyone have any experience with loft extensions and able to confirm whether the 270mm will ultimately need to be pulled up.?

Many thanks in advance chaps

fly high · Apr 16, 2024

You loose more heat through the roof than walls so more cost effective. For floors between storeys you would fit 100mm of insulation between joists for sound so some can be left. The whole area won't be used for a loft conversion so can be left. For the roof itself new insulation would be below and between. Between you could use the existing mineral wool rolls, generally no more than 100mm leaving min 50mm ventilation gap above it.
For cavity walls blown mineral fibre shouldn't cause a damp problem.

beorhthelm · Apr 16, 2024

loft first, pointless to do walls without it. it's relatively cheap and DIYable if willing (pick a cool day though, some masks, gloves, stanly knife). insulation can stay or be reused on a conversion.

schmunk · Apr 16, 2024

Loft insulation is surely the first choice - it's cheaper, easier (self-fit!) and and has the most benefit.

As above, if he buys 100mm and 200mm rolls of insulation, the 100mm can be retained as 'under-floor' insulation in future.

Total for 300mm will be less than £10/m² - just how much is he going to need?

Bold Seagull · Apr 16, 2024

I'd echo the above. If you do cavity wall insulation, the loft works will invariable involve some work around the external walls and there is a risk of dust and debris falling into the cavity, settling on the insulation and providing a route for damp to penetrate. If you know works are going to happen at a later date that might involve the external walls, don't do the cavity wall insulation first, do that after all other works have been completed and ensure the cavity is clear.

shingle · Apr 16, 2024

Thanks everyone for the advice

Justice · Apr 16, 2024

beorhthelm said:
loft first, pointless to do walls without it. it's relatively cheap and DIYable if willing (pick a cool day though, some masks, gloves, stanly knife). insulation can stay or be reused on a conversion.

A bread knife is the best tool for cutting loft insulation.

Justice · Apr 16, 2024

shingle said:
Good morning all

Just posting a question on behalf of my eldest son who has just bought his first house. The property is currently uninsulated and he's trying to decide between cavity wall and 270mm loft insulation. He can only stretch to getting one of them done. He's read some horror stories about cavity wall causing damp issues and so is inclined to go for loft insulation. However, in around 5 years time he is looking to get loft a loft extension and so hes not sure whether loft insulation is a good investment if its the case that loft insulation will ultimatly need to be pulled up and discarded.

Does anyone have any experience with loft extensions and able to confirm whether the 270mm will ultimately need to be pulled up.?

Many thanks in advance chaps

The loft extension should be insulated with kingspan or similar product. I would imagine they would also renew the floor insulation as it will be pulled up anyway as you need a steel, wiring and plumbing all routed within the floor space.

For the existing you could kingspan all the outside walls and forget about cavity insulation. You will lose and inch or so although it’s a price work paying.

Bodian · Apr 16, 2024

Like the others - go for the loft. Made a noticeable difference when I first did mine.

But wear a mask and paper suits - it's bloody horrible stuff.

Also, check out the availabilty of grants https://www.gov.uk/apply-great-british-insulation-scheme

Whitley Bayster · Apr 16, 2024

The weakest thermal elements of a house are the openings. Changing windows and doors to high performance double or triple glazed types makes the biggest dfference but its expensive. Roofs are next and it is the cheapest and easiest improvement to make. Probably about 300mm is a good starting point for effective insulation in an older house with insulation laid between joists and then laid in the opposite direction over the top. Its important to get across the whole area so fully into the eaves and insulate the loft hatch otherwise you lose a significant part of the benefit. External wall would be next and then the ground floor. A key consideration with older houses is that you are taking a relatively leaky unsealed proerty and gradually making it more and more air tight. You are losing the natural air changes so having some form of background ventilation becomes more important the more you insulate. If you are just insulating the loft that's not something you have to worry about

shingle · Apr 16, 2024

Thanks very much everybody for your detailed advice

fly high · Apr 16, 2024

Whitley Bayster said:
The weakest thermal elements of a house are the openings. Changing windows and doors to high performance double or triple glazed types makes the biggest dfference but its expensive. Roofs are next and it is the cheapest and easiest improvement to make. Probably about 300mm is a good starting point for effective insulation in an older house with insulation laid between joists and then laid in the opposite direction over the top. Its important to get across the whole area so fully into the eaves and insulate the loft hatch otherwise you lose a significant part of the benefit. External wall would be next and then the ground floor. A key consideration with older houses is that you are taking a relatively leaky unsealed proerty and gradually making it more and more air tight. You are losing the natural air changes so having some form of background ventilation becomes more important the more you insulate. If you are just insulating the loft that's not something you have to worry about

Need to be careful at the eaves, don't block any ventilation at the eaves so not fully into eaves. Cross ventilation must be maintained to prevent condensation.

raymondo · Apr 16, 2024

fly high said:
Need to be careful at the eaves, don't block any ventilation at the eaves so not fully into eaves. Cross ventilation must be maintained to prevent condensation.

Yep, a neighbour insulated his loft right up to the eaves, blocking his eave grill vents (they were hard to see to be fair) and he got a lot of condensation.

fly high · Apr 16, 2024

raymondo said:
Yep, a neighbour insulated his loft right up to the eaves, blocking his eave grill vents (they were hard to see to be fair) and he got a lot of condensation.

House round the corner had insulation badly installed in the 70s, closed off the eaves, ended up with dry rot in the roof.

Bozza · Apr 16, 2024

We paid a fair bit for cavity wall insulation last year.

Now, I certainly wasn't expecting any kind of transformational "Oooooh - isn't this toasty" now kind of feeling, but if it has made any difference, it has to be very marginal.

I've certainly got buyer's/well-that-feels-like-a-complete-waste-of-money remorse

Curious Orange · Apr 17, 2024

Bozza said:
We paid a fair bit for cavity wall insulation last year.

Now, I certainly wasn't expecting any kind of transformational "Oooooh - isn't this toasty" now kind of feeling, but if it has made any difference, it has to be very marginal.

I've certainly got buyer's/well-that-feels-like-a-complete-waste-of-money remorse

We had it installed in the two walls of our study extension that had cavities, and I'd agree that the difference is marginal - it's gone from f'ing freezing to cold!

I didn't bother with the cavities on the main building, though when we had our new extension added that was obviously built to modern standards and you can tell it is warmer when you move into it.

I really must get around to finishing the loft insulation refresh...

clivebuckley · Apr 18, 2024

Justice said:
A bread knife is the best tool for cutting loft insulation.

I used to have a loft insulation business and that's what I used, also best tool for cutting pipe insulation

clivebuckley · Apr 18, 2024

All the advice given is really good, the other thing your son has to do is make sure he insulates any pipes or laps the insulation over the pipes to stop them freezing.
Loft insulation is an easy job, wear knee pads and preferably do it with 2 people, one in the eaves rolling the material towards the middle and the other cutting and passing rolls to you.
Less moving around then and so less chance of putting your foot through the ceiling!

Westdene Seagull · Apr 18, 2024

Definitely loft first - fairly cheap and DIY job ( with the correct protective clothing ). If we ever get decent snow again you can see houses that have it and those that don't. Maybe your son should talk to his energy supplier about the cavity insulation - some still have government funds to help with the cost - or even for free depending on circumstances ( we got ours done for free by EDF a few years ago ).

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