[agentorange]

What's the deal with new builds, do they get cavity insulation, or do they rely on insulating breeze blocks as the inner layer?

When I was visiting family in the UK in June, I heard stories that cavity wall insulation was no longer in favour. Is it related to the insulation breaking down after 20-30 years and creating damp issues, or were a lot of places done when really it was always going to cause problems.

What's the story on attic/roof structure ventilation in the UK these days. I was looking at the roof of one house I stayed in and could not see any soffit vents or ridge vents. How does that work?

[pmgreenwood]

I am very interested in this issue as it applies to all uk houses with cavities including my own mid 50's bungalow. Looking at the figures, cavity wall insulation would appear to be the one remaining energy efficient I could do. However, when I do a Google search locally for "Cavitt wall insulation" the search produces more firms taking it out than installing. This reduces any confidence in going ahead

[HighlandPete]

Originally Posted by agentorange

What's the deal with new builds, do they get cavity insulation, or do they rely on insulating breeze blocks as the inner layer?

When I was visiting family in the UK in June, I heard stories that cavity wall insulation was no longer in favour. Is it related to the insulation breaking down after 20-30 years and creating damp issues, or were a lot of places done when really it was always going to cause problems.

What's the story on attic/roof structure ventilation in the UK these days. I was looking at the roof of one house I stayed in and could not see any soffit vents or ridge vents. How does that work?

It's a bit of a minefield here in the UK.

Many homes have been insulated in the cavities and roof area and rot and damp has set in.

As the above post... many are having to have insulation taken out. Often folks can't get a mortgage, if the roof space has the spray on insulation.

[ian332isport]

I’m not 100% on this, but believe it’s only been a problem where the polystyrene bead (think bean bag filler) is used. This is what seems to be installed more recently where people have had grants for home insulation.

I think it’s because of the smooth surface of the polystyrene beads. It allows condensation to form, and capillary action causes it to track through to the inner walls and causes damp.

Thankfully this sort of installation can be vacuumed out, which is what most of these companies are doing.

Our house was built in the 80’s and has what looks like some sort of fibre based material. We’ve never had any damp issues. My in-laws had the polystyrene beads installed in a previously dry house and very quickly had damp coming through.

[Pond]

I am an amateur builder (it's a weird hobby), having built two houses from scratch and many extensions. Here's how it works:

The answer to the original question is yes, new builds are still using cavity insulation and traditional rockwool/ fibreglass in the roof space. The only real change in the last few years is that new builds require the floor to be insulated, usually under the screed.

Cavity walls were introduced in the c1940s, as a solution for damp, not for insulation. The standard was, and still is to a degree, 50mm gap between the 'leaves'. Wall ties are used to tie the 'leaves' together. These were then altered to incorporate a 'drip' in the centre (usually a bend in the tie) to prevent moisture tracking along the tie to the inner leaf.

Cavity insulation was adopted in the c1960s. This involves cavity 'batts' (standard size sheets of rockwool/ fibreglass insulation) laid against the inner leaf of the masonry with an air gap of at least 20mm to the outer leaf; to prevent moisture tracking. The wall ties were then fitted with a grip to hold the batts in place and stop them falling into a big heap.

In the last 20 years or so, solid cavity insulation batts have become available, these are 'celotex' type, ie solid foam with foil backing. They give much higher insulation values but are much more expensive than traditional rockwool.

One problem with cavity insulation is that bricklayers always fit it, as it goes in as the masonry is laid. Bricklayers are always on piece work so faster makes more money. They also have little knowledge of what the insulation is required to do so don't install it very well. Once finished no-one is ever going to see it again, either.

Retrofitting cavity insulation, ie drilling a few holes at various points and 'squirting' some kind of insulating material (be it poly beads, foam, even paper pulp), is not good, as it will fully fill the cavity, there is no way of it not, and give moisture an easy path to track from outside to inside.

Insulation is good, moisture is bad in a building. The hard part is doing one properly and effectively without the other being a problem. It is quite simple to achieve on a new build if you understand it and install everything correctly. The last two parts are where the problems can lie, as housebuilders are not known for their attention to detail.

Soffits and fascias are just one way of venting a roof void. There are others (ridge vents is one of many) and generally depend on design of the building which are utilised.

[Tengocity]

I looked in to this recently and have indeed still gone ahead with it. The thing that's clear is the suitability of the property itself has to be right. Many of the issues are older properties, and houses with questionable build quality, and also where they're exposed to high levels of driving rain.

The latter is something I have to be mindful of where we live, so I'll be making sure the render is well looked after and remains in excellent weatherproof condition.

Having it fitted will save us hundreds of pounds a months during winter, so on balance we felt it was the right thing to do. If damp was an issue in one spot then it could be rectified relatively easily.

A few minutes googling any of the foam insulations and it's clear they're a minefield. I think with sensible application they could make sense in some situations, but they get flagged on surveys and many lenders won't give a mortgage unless it's removed to allow inspection of the roof. I'm not sure I understand that particularly as lots of roofs are not easily inspected, for example when someone has done a loft conversion.

[HighlandPete]

Originally Posted by Tengocity

A few minutes googling any of the foam insulations and it's clear they're a minefield. I think with sensible application they could make sense in some situations, but they get flagged on surveys and many lenders won't give a mortgage unless it's removed to allow inspection of the roof. I'm not sure I understand that particularly as lots of roofs are not easily inspected, for example when someone has done a loft conversion.

I understand it's the difference between whether the damp comes through and is more easily noticed, or the type of insulation (spray on types) which virtually seal in the damp around roof joists, etc., completely hiding damp and leaking roof issues until it is too late.

[agentorange]

Originally Posted by Pond

One problem with cavity insulation is that bricklayers always fit it, as it goes in as the masonry is laid. Bricklayers are always on piece work so faster makes more money. They also have little knowledge of what the insulation is required to do so don't install it very well. Once finished no-one is ever going to see it again, either.

It's not just bricklayers. The houses here are timber framed with stucco covered plywood on the outside. The "cavity" is supposed to be filled with batt insulation. Some Northern states do spray in foam.

Friend had a bunch of upgrades done on his bathroom that meant removing the interior drywall. That revealed a patchwork of insulation between the vertical timbers and the horizontal pieces in there, and this was on a South facing wall in the SW deserts of the US. He was pretty pissed. He also realized that the insulation on the East facing knee wall to a void over the garage was only two inches (50mm) thick and that the void was not sealed off from the outside by any wallboard. It was loose enough for him to see daylight coming through the joints in the fascia of the little piece of roof. All he could do was jam in some thicker insulating batt to try and seal off the void.

He asked the contractor doing his work if he had seen anything like it before. The guy looked him in the eye and said, "You got lucky. I've seen entire walls uninsulated and those knee walls are never skinned on the outside like they would be up North. The insulation you found in there was a bonus in this city."

I think what we need are some videos on Youtube of builders getting their knees drilled for their transgressions as examples to the rest. Maybe that would improve the quality a bit.

[Pond]

Maybe one good thing coming from the 'energy crisis', is that ordinary people who otherwise wouldn't have cared about 'global warming', are actively looking at ways to improve their home's efficiency.

When it hits you in the pocket, it's amazing how we can step up.

If I were a 'conspiracy theorist', which I'm definitely not, I would say this may have all been engineered to save the planet (no scrub that, save the human race, the planet will do just fine without us).

[Watsey]

We had polystyrene bead cavity fill insulation installed (blown) when we had our 1930s house gutted and extended 12 years ago.

The beads are coated in dry adhesive and are blown into the cavity along with a water mist which allows the adhesive to stick the beads together once they have formed a 'full fill' of the cavity.

The insulation has made a massive difference in summer and winter, and we've not had any problems with damp.

Whether any moisture in the former cavity space (now filled with insulation) forms due to the outer skin of the cavity wall construction becoming wet/saturated, or interstitial condensation forming as moist air cools as it passes from inside the house into the insulation, it's important that anything within or bridging the cavity doesn't promote damp forming on inside surfaces of the external walls.

Contrary to an earlier post, the poly beads are intended to allow water to trickle downwards through the cavity rather than across the cavity (gravity being stronger than capillary action horizontally).

Blown fibre insulation gained a bad reputation for causing a lot of problems. Moisture could soak the fibres which caused moisture to bridge the cavity, and the fibre material settled over time which caused cold patches where the cavity became a void once more.

Roof insulation and venting typically depends simply on whether the roof space is to be uninhabited (cold) or inhabited (warm) Insulation and ventilation will always be required, but the placement and materials can be quite different.

[NanasBack]

Minefield...

Our first house was a timber framed construction. A Canadian design.
It had warm air central heating with an unvented loft / roof space.

We had a problem develop after a few years, with water drops / stains appearing on the bedroom ceilings occasionally. Only happened maybe every couple of years or so.

Enquiries to various roofers as to what the problem could be, resulted in quotes :-
1. Felting needs replacing - So off with the roof tiles. Replace felting. Replace roof tiles.
2. The tiles have gone porous, need new felt and roof tiles replacing.

I didn't believe either was the required solution.
Whenever it rained heavily, looking in the loft showed no signs of rain or water.
Had the ridge tiles re-pointed anyway.

It took years to figure out what was happening.

I believe the problem had been caused by gradual changes over the years.
Added a shower in the bathroom. (No vent fan, just opened a window).
Tumble drier, dish washer.
Double glazing.

So, all things which increased the general humidity in the house.
The original windows were always streaming with water.
Double glazing stopped that.
But where was all that water / humidity going?

Apparently, up the loft.

Tried to work out what the possible cause was. Noticed once, it felt humid in the loft.
Testing with a hygrometer revealed the humidity in the loft was 99%, - for 99% of the time.

Eventually realised that, when there was a real winter cold spell, the humid air was condensing on the inside of the roof tiles and raining down on the fibre glass loft insulation.

The insulation would soak up the water and contain it for a day or so, up to the point where, if it became saturated, then water may appear on the bedroom ceiling.

Looking in the loft revealed water sodden insulation, but it hadn't been raining for days.
It may also be 'warm' outside at this time.

Prior to realising the humidity issue / cold spell, it didn't make sense.

A neigbour had a copy pf the building plans for the house.
Looking at these, the loft design was sealed, but there was one obvious difference.
The plaster board ceilings shown on the design plans had an aluminium foil backing for bedroom ceilings.
Those installed did not have the foil.
I guess the foil would have prevented a lot of humidity rising into the loft in the first place and may have prevented the issue ever happening.
It would also have reduced the likelyhood of water penetration from accumulated water.

To test the humidity theory, one vented ridge tile and a number of plastic sofit vents were fitted.

Problem solved for £50, rather than thousands, the other methods would have cost.
And the problem would still have been there!

[agentorange]

Originally Posted by NanasBack

A neigbour had a copy pf the building plans for the house.
Looking at these, the loft design was sealed, but there was one obvious difference.
The plaster board ceilings shown on the design plans had an aluminium foil backing for bedroom ceilings.
Those installed did not have the foil.

Somebody should have spent a week screaming, staked out over a fire ant hill with their balls in a vice for that screw up. Building a house is not an "error and omissions excluded" (EOE) endeavor.

Now you have a roof structure operating in a way that it wasn't designed to. In the winter, the attic will now be freezing cold over the top of your insulation. As it was supposed to be built, the attic would have acted as a buffer, retaining any heat absorbed during the day, either from the house or any sun during the day.

My attic is ventilated because it has the gas heaters up there, as most builders here have never heard of balanced flue gas systems. Given the way the rest of the house leaks, that's a pain. Either cold air I don't want is getting in (winter), or cold air I do want is getting out (summer).