Cavity Insulation

[Woody2Shoes]

Hi,

the existing construction really does matter - including whether it is of special designation (listed, in a conservation area etc. etc.).

There are two things that make a house built before about 2003 feel cold:
- draughts (down chimneys, through floorboards, through brick walls [yes really!], through windows and doors);
- heat loss through radiation (and convection, besides the draughts).

The biggest problems potentially caused when you take steps to address the above problems are:
- Increased dampness/condensation within the structure https://en.wikipedia.org/wiki/Interstitial_condensation - it's important to maintain proper ventilation even in an "airtight" house! One classic is when insulating a roof, failing to allow air to circulate in and out of a cold roof-space, causing damp in the loft.
- Bridging rain barriers, when adding insulation [esp. when filling a cavity, which is primarily a rain barrier] allowing wind-blown rain to flow directly through walls. I have seen this at first hand. A masonry wall will protect you against windblown rain UNTIL it becomes saturated with water [this may take a particularly bad period of weather where the wall can't dry out in between successive storms] at which point a very small pressure difference across it [i.e. even a light wind] will push vast amounts of rain though it.

My priorities would be:

- Roof insulation;
- Draughtproofing (combined with proper ventilation) - possibly at the same time as insulating any suspended floors;
- Depending on the construction and design details/quality of the house, insulation externally [e.g. under render or tile/timber cladding] or internally [e.g. a new layer of insulated plasterboard] leaving the existing cavity to serve as a rain barrier. Internal and external insulation both have their pro's and con's especially when trying to avoid cold-bridging.

It's important to remember that most of the work is likely to be covered by Building Regs. and it would probably be worth talking to a building inspector at a fairly early stage.

Cheers, W2S

 

[jimmy_s]

I'm opting for100mm internal insulation between the studs. 60 sheets of Kingspan seconds are on their way.

I'm going to be doing something similar to you Roger. Our house is a mixture of stone and cavity walls some of which are insulated and some not. In some rooms I may go for the actis foil insulation.

Before any of that happens I am going to get rid of some suspended timber floors and infill/ to make a groundbearing slab. I can't get proper solum ventilation in place under these floors due to the way the previous owner has carried out an extension. If I insulate between the floor joists in this case I will most likely end up with interstitial condensation.

 

[Lons]

Is there a gap between those studs and the masonary Roger?, Difficult to see from the photo.

We did similar with a grade 2 listed stable conversion some 12 years ago, outer walls were 600 thick stone, we kept an approx gap of 50 mm ( uneven walls ) constructed the stud walls in sections on the floor, stapled a breathable membrane to the back and fixed in position top and bottom. Then fitted the Kingspan, we used 90 mm as the studs were PAR ex 100 x 50 and 100 mm kingspan would be too thick.

Results were excellent, building inspector was happy and my customer has a very warm house.

Bob

 

[RogerS]

Is there a gap between those studs and the masonary Roger?, Difficult to see from the photo.

We did similar with a grade 2 listed stable conversion some 12 years ago, outer walls were 600 thick stone, we kept an approx gap of 50 mm ( uneven walls ) constructed the stud walls in sections on the floor, stapled a breathable membrane to the back and fixed in position top and bottom. Then fitted the Kingspan, we used 90 mm as the studs were PAR ex 100 x 50 and 100 mm kingspan would be too thick.

Results were excellent, building inspector was happy and my customer has a very warm house.

Bob

A good point, Bob, but fortunately loads of room there.

And we're flying a flag today as it's the second day without rain. =D>

 

[transatlantic]

Hi,

the existing construction really does matter - including whether it is of special designation (listed, in a conservation area etc. etc.).

There are two things that make a house built before about 2003 feel cold:
- draughts (down chimneys, through floorboards, through brick walls [yes really!], through windows and doors);
- heat loss through radiation (and convection, besides the draughts).

The biggest problems potentially caused when you take steps to address the above problems are:
- Increased dampness/condensation within the structure https://en.wikipedia.org/wiki/Interstitial_condensation - it's important to maintain proper ventilation even in an "airtight" house! One classic is when insulating a roof, failing to allow air to circulate in and out of a cold roof-space, causing damp in the loft.
- Bridging rain barriers, when adding insulation [esp. when filling a cavity, which is primarily a rain barrier] allowing wind-blown rain to flow directly through walls. I have seen this at first hand. A masonry wall will protect you against windblown rain UNTIL it becomes saturated with water [this may take a particularly bad period of weather where the wall can't dry out in between successive storms] at which point a very small pressure difference across it [i.e. even a light wind] will push vast amounts of rain though it.

My priorities would be:

- Roof insulation;
- Draughtproofing (combined with proper ventilation) - possibly at the same time as insulating any suspended floors;
- Depending on the construction and design details/quality of the house, insulation externally [e.g. under render or tile/timber cladding] or internally [e.g. a new layer of insulated plasterboard] leaving the existing cavity to serve as a rain barrier. Internal and external insulation both have their pro's and con's especially when trying to avoid cold-bridging.

It's important to remember that most of the work is likely to be covered by Building Regs. and it would probably be worth talking to a building inspector at a fairly early stage.

Cheers, W2S

Thanks.

As mentioned, I''m definitely going to get the roof insulation done and go from there. Even if it provides a small improvement, I think it will be enough for me to forget about the walls.

 

[graduate_owner]

Insulating the inside sounds very sensible and certainly safer than cavity wall insulation but check out issues of dew point and interstitial condensation within the solid wall or internal leaf of a cavity wall. Just something I read a while ago when I was thinking of adding some insulation to my house.

I seem to remember also that if you decide to insulate your walls, you must ( according to local authority regs) bring the walls up to current spec. So strictly you are not allowed to add SOME insulation and save energy. You have to go the whole hog or do nothing - how stupid is that? Of course, the local council do not HAVE to be informed!!

Please note I am not an architect or surveyor, so don't take all the above as totally correct - check it out yourself.


K

 

[RogerS]

Yes, my read of the regs is that even if you want to render the external wall of a house then you have to add insulation.

 

[WellsWood]

Pretty sure we all know that heat rises, yeah? So how can 80% go sideways?

Well, not wishing to be overly pedantic, but not really. Hot air rises, as it is less dense and lighter than cold air, but heat itself doesn't care which way is up and wil cheerfully migrate to any colder surface such as a wall or window. In this regard, hot air rising makes things worse as the air that cools (next to a cold wall for example) will constantly be replaced by warmer air through convection. If I remember my physics correctly the rate of exchange of heat energy between two objects increases with temperature differential (it has been a long time though).

 

[Lons]

Pretty sure we all know that heat rises, yeah? So how can 80% go sideways?

Well, not wishing to be overly pedantic, but not really. Hot air rises, as it is less dense and lighter than cold air, but heat itself doesn't care which way is up and wil cheerfully migrate to any colder surface such as a wall or window. In this regard, hot air rising makes things worse as the air that cools (next to a cold wall for example) will constantly be replaced by warmer air through convection. If I remember my physics correctly the rate of exchange of heat energy between two objects increases with temperature differential (it has been a long time though).

Absolutely correct as far as I remember as well though possibly even longer ago than you. :lol: This is backed up by the general published figures for heat losses from non insulated domestic dwellings and although those vary a little and some show losses from draughts and chimneys while others don't the consensus is that around 10% more heat is lost through the walls than the roof. neither do they differentiate between single and multistory buildings but it is a guide.

Having said that, the loft is the most cost effective and easiest area to improve.

A typical simplified illustration!

 

[BearTricks]

A friend had some done on what I believe is a fairly old house. It's the injected type and it has been a nightmare for them. I believe they've got the cold spots that Mike talks about and they're getting damp all over the place.

My mum had the polystyrene beads pumped in to a late 19th century house. Ended up with beads appearing all over the place which can't be good for the environment and I dread what happens if they knock somewhere full of beads down.

 

[dean0866]

In the mid 80s I used to install cavity wall insulation for a living. What I can say is there are many factors to take into account when determining whether it's a good idea or not but a lot of the horror stories you read about are down to a poor product being installed regardless of the suitability of the property and installed badly. As an example, a couple of people here have mentioned polystyrene beads and how they get everywhere..........they do if they are pumped into a cavity without a suitable bonding agent. Trust me, I know . I had to drain two detached houses where some ***** had pumped them in dry. We used to use Rockwool as our main product and as long as you did your property review properly, used a very good and close drilling pattern and didn't cut corners, you'd have very few issues. Most issues we encountered were down to poor building practices not the fault of the insulation. When I say poor building I mean cavities full of rubble or large bridges across cavities. Most of these issues could be remedied quite quickly. We were quite lucky as we were equipped with a borescope so could look in the cavities before starting the job. I rejected many a house because of the poor quality of the cavity and the bridging, the worst, had 8 courses high of rubble around the base of all the outer walls. I thought it was a solid construction at first glance. Anyway, it was a long time ago and I guess installation techniques and materials have changed quite a lot since then.

 

[Lons]

That's spot on Dean and as an ex builder I came across many instances of very poor workmanship, in fact the house I bought before my current home was new and I made the builders take stone out to clear the cavity around the whole perimeter of the building. Problems of this nature were caused primarily because teams of brickies were paid piecework on the number of bricks laid in a day and were poorly supervised by their own company as well as building inspectors.

Modern cavity construction incorporates insulation as you build and largely prevents mortar bridging but still needs care to do it properly.

With regard to that, my current home which was 8 years old when I bought it had a damp problem which I found to be due to the builders having not put the required cavity trays over the windows. It took serious threats to sue the surveyor and the NHBC who dragged their heels on the 10 years warranty to eventually get the remedial work done, at great expense. Clearly they didn't put the poly beads in correctly either.
When I asked the building inspector why he passed the construction he said " I can't be everywhere, you just have to trust them" :roll:

cheers
Bob

 

[MJP]

I know that this is an old thread, but I might be able to make a constructive contribution.
I live in an old detached stone house, 22" thick solid walls. My pine end faces North, gets sun only for a few days in high summer (if that!) and is lashed by rain.
It was by far the coldest wall in the house, and made the room almost unusable.
I had the wall externally clad with 50mm insulation, then overlaid with a stipple finish and the house was transformed - the wall is now warm and it acts as a huge storage heater. The room has gone from frigid to cosy, whatever the weather.
Of course, a 2ft thick stone wall contains a lot of water, and this has to dry out before the wall warms up - we had a dehumidifier running constantly for two years to dry it out properly, but the transformation is way beyond what we had hoped for.
I would go for external insulation every time - and you gain a storage heater into the bargain!

Martin.

 

[transatlantic]

I know that this is an old thread, but I might be able to make a constructive contribution.
I live in an old detached stone house, 22" thick solid walls. My pine end faces North, gets sun only for a few days in high summer (if that!) and is lashed by rain.
It was by far the coldest wall in the house, and made the room almost unusable.
I had the wall externally clad with 50mm insulation, then overlaid with a stipple finish and the house was transformed - the wall is now warm and it acts as a huge storage heater. The room has gone from frigid to cosy, whatever the weather.
Of course, a 2ft thick stone wall contains a lot of water, and this has to dry out before the wall warms up - we had a dehumidifier running constantly for two years to dry it out properly, but the transformation is way beyond what we had hoped for.
I would go for external insulation every time - and you gain a storage heater into the bargain!

Martin.

Ah - glad it worked out for you. To be honest, I have been completely put off the idea - too many horror stories. I have decided to just accept the fact that I won't be living in this house indefinately and to suck up the few hundred extra a year to heat it. External sounds like the way to go, but I don't think it would work to well with a semi-detached house would it? unless you did both at the same time.

 

[MJP]

No, you're right, it would be best to have both houses done at the same time - apart from anything else, it would look odd if only one were done.

I went around looking at houses that had been insulated in this fashion before deciding to get ours done, including a number of semis. It does look good when done properly and the householders were unanimous in their satisfaction.

The procedure has become popular in recent years and this has attracted the cowboys, so it's important to use a builder who can give you addresses of houses that he's already done so that you can go around and take a look-see.

It's not a cheap process either, so if you're expecting to move in a decade or so it might be cheaper to just pay the extra on the energy bill!

Martin.

 

[transatlantic]

It's not a cheap process either, so if you're expecting to move in a decade or so it might be cheaper to just pay the extra on the energy bill!.

Yep - that is my logic. Curious though, how much was it for you? and what size of house? did you have to consult your insurance company or anything?

 

[MJP]

Well, it was four or five years ago now and I live in the very wet Swansea Valley in South Wales.

Total cost was £4500 - but that included removal of a big brick chimney, replacing it with one of those hideous "Steamboat Bill" tin stacks, and extending the eaves out far enough to cover the top of the insulation, to keep the rain off the top.
Removal of the chimney costs around a grand around here, I guess extending the eaves may be £500/600 or so, so the actual insulation job was somewhere just short of £3000 I suppose.

It's a biggish detached house - 45ft frontage, four bedroom, solid stone walls, 1901 vintage: typical of this area.

The only contact with officialdom was a visit from the building regs officer from the council - a five minute visit which cost me £100 (from memory) and to rub salt in the wound the council later sent me a form asking what I thought of the value for money from his visit.

I did try to control myself when I answered, but was unsuccessful.

As far as a strictly financial value is concerned, it's questionable whether it's worth doing - if you save £200 a year on energy bills it would take 15 years or so to pay back - but as far as quality of life is concerned, it's a no-brainer.

I would do it again, without hesitation.

Martin.

 

[transatlantic]

Well, it was four or five years ago now and I live in the very wet Swansea Valley in South Wales.

Total cost was £4500 - but that included removal of a big brick chimney, replacing it with one of those hideous "Steamboat Bill" tin stacks, and extending the eaves out far enough to cover the top of the insulation, to keep the rain off the top.
Removal of the chimney costs around a grand around here, I guess extending the eaves may be £500/600 or so, so the actual insulation job was somewhere just short of £3000 I suppose.

It's a biggish detached house - 45ft frontage, four bedroom, solid stone walls, 1901 vintage: typical of this area.

The only contact with officialdom was a visit from the building regs officer from the council - a five minute visit which cost me £100 (from memory) and to rub salt in the wound the council later sent me a form asking what I thought of the value for money from his visit.

I did try to control myself when I answered, but was unsuccessful.

As far as a strictly financial value is concerned, it's questionable whether it's worth doing - if you save £200 a year on energy bills it would take 15 years or so to pay back - but as far as quality of life is concerned, it's a no-brainer.

I would do it again, without hesitation.

Martin.

Yep - if it makes you happy, well worth the money.

 

[graduate_owner]

Just wondering - if you used polystyrene beads without a bonging agent, would you be able to remove them more easily in the event of subsequent damp problems? With a bonding agent, wouldn't they set into a solid, permanent mass?

K

 

[dean0866]

The bonding agent bonded them enough to hold them together, not really a solid mass so to speak. No bonding agent, the beads come out of every small hole around the house, covering gardens and filling up internal cupboards etc forever and a day. It looked similar to snow but not as much fun.