New build: Solid walls vs cavity walls

[Sjk]

Not sure if it’s ridiculous to consider solid walls for a new build.

 

I have done a lot of googling on the subject, it seems you can get a decent U value without the wall being too thick, some suggesting even thinner than would be required with cavity walls!

 

Im considering it because there is a flood risk, and I believe solid walls are preferable in this situation, water in the cavity wouldn’t be pleasant even if I chose closed cell insulation. 

 

Other positives could be, depending on route chosen, dense block work could be a great sound barrier, or it opens up the possibility of more interesting brick bonds. Have double the bricks would be pretty expensive though. 

 

I can’t work out if condensation is a risk, some people say it is a risk with solid walls, others think cavity wall insulation will be the next ppi for its damp risks..

 

That brings me on to the next thing internal or external wall insulation, it seems external is preferable, however internal offers the chance to have more interesting brick work. In my mind I think external would be more effective, however with external surely you will lose a lot of energy heating the dense blocks? You wouldn’t have this with internal insulation. 

 

Hmmm. Going around in circles with this one!

[Declan52]

You can go with a single skin option using blocks on their flat and combine this with external insulation which you then render what ever colour you want which will then be waterproof. 

The problem with using bricks is they aren't waterproof so will pull water in towards the house,  hence a cavity would be needed to stop the damp going all the way in. 

With blocks they will store the heat and then slowly release it back. 

[Sue B]

Why not look at ICF then?  In effect you have solid walls with the insulation all in place?

[Nick1c]

Try googling 'Tony's house reading' for an example of a solid walled house. 

If there is a significant flood risk how will you manage it - raising the ground floor?

will it be insurable?

[Ferdinand]

10 hours ago, Sjk said:

 

 

I can’t work out if condensation is a risk, some people say it is a risk with solid walls, others think cavity wall insulation will be the next ppi for its damp risks..

 

That brings me on to the next thing internal or external wall insulation, it seems external is preferable, however internal offers the chance to have more interesting brick work. In my mind I think external would be more effective, however with external surely you will lose a lot of energy heating the dense blocks? You wouldn’t have this with internal insulation. 

 

Hmmm. Going around in circles with this one!

 

I think you need to approach these two through your wider design goals rather than as more standalone questions ... how much heat storage capacity do you need in the structure, and what is your planned route and method for letting any moisture out of your walls. That in turn depends on the type of structure you select, and interplays with it. You need to be looking at thermal spec, decrement delay, and so on.

 

eg for EWI it will impact o; permeability and wall thickness whether you choose PIR or EPS.

 

Ferdinand

 

Edited February 26, 2019 by Ferdinand

[Sjk]

Thanks I’ll have a look at Tony’s build. 

 

ICF, I have to say I didn’t really give it much consideration before as I thought it may cause problems being a more unusual construction method. 

 

Flood risk, well it’s never flooded but with tail end risk plus climate change it could, with the EA wanting the FFL 600mm above this figure it’s not going to be an option to Elevate the house much and definitely not to the EA level.  

 

At the moment I’ve only been looking at u values, the solid wall idea is a new ish one after someone posted. 

[MarkyP]

I think Tony's house (if we're talking about the same one!) is fully fulled wide cavity, similar to the Denby Dale passive houses.

 

cavity walls as built new I think is still very much a standard and I think low risk in terms of later problems, the claims you mention will be for retrofit cavity wall insulation and damp issues (it's a complex topic) but this isn't something that put me off a wide fully filled cavity in my extension. Cavity walls aren't as popular with self builders, particularly passive houses. However it can be done well.

 

solid wall is an option I considered. Mortgage-ability is a factor, you may need an eye on a future sale and there can be a bit of "computer say no" from lenders against single skin walls. Admittedly this probably isn't aimed at well built new houses with wide format blockwork, rather at single skin brick walls built last century which lenders consider structurally unsound. However, it may be worth exploring to check you wont get caught up in the same bucket.

 

Wide format blocks and EWI would be my preferred approach for single skin. EWI can be employed achieving what is called the "full tea cosy" method - a continuous insulation layer from footing all over the house, including roof (using warm roof approach). You can completely eliminate structural cold bridging. EWI can be rendered, timber clad (or any cladding - zinc, through coloured cement panels, etc) or even faced with brick slips (these are effectively slithers of brick applied like tiles with a mortar applied rather like grout). I have seen some high spec examples that looked incredible and you would never have guessed they weren't brick walls.

 

IWI is a bit of a headache with condensation risk behind the insulation, and the issue of creating cold bridges with internal structural timber piercing through the insulation layer to the outer structural wall. It's typically a retrofit approach, not sure I've ever seen it employed new build.

[Roger440]

You can get cavity wall insulation that goes in as a liquid and then becomes, effectively expanding foam. Aside from some of the obvious advantages, it fully waterproof and ones of its claimed features is for use in flood prone houses. So it would be full fill and flood proof. Arguably, you could just do the 1st meter, then normal cavity insulation from thereup. Its expensive! https://www.completeinsulations.ie/spray-foam-cavity-wall-insulation/

[Oz07]

Looks good what kind of money per m2? Does this replace need for parge coating?

[Sjk]

Thanks peeps, still mulling this over at the moment.

 

 

[Nick1c]

@MarkyP sorry, my mistake, I remembered it as you describe your tea cosy option. Isn't EPS good in damp situations? 

[MarkyP]

I'm no expert on approaches to flood mitigation but thinking out loud I could see tea cosy approach being preferred over cavity. I think you would certainly want to avoid mineral wool in the cavity if there was a risk the cavity could be breached during a flood. The stuff takes an age to dry out once wetted (experience of dritherm32 batts left in the rain on my site) and when saturated tends to slump and deform. 

 

If going with EWI, then I would think an open cell insulation would be much preferred. EPS is open cell somewhat vapour open so in a flood the wall inside if wetted would be able to dry outward. Closed cell such as PIR or XPS I think would not allow this, you'd need to dry from the inside only. I think there are few system suppliers who specify closed cell EWI in any case. There were issues a while back with PIR boards used for EWI deforming once fixed, "pillowing" I think was the term used. Nearly all systems I considered were graphite enhanced EPS. There are some that offer wood fibre or mineral wool options but neither would be suitable where there was a risk of water immersion. I learned that EWI grade EPS differs from standard stuff. EWI grade it is cut from aged EPS blocks which are dimensionally stable. Standard EPS is not and there is a theoretical risk the boards could deform causing cracks.

 

 

[Mr Punter]

We are in a flood zone and I have used brick and med density block cavity with Celotex CF5000 rigid insulation. Internal partitions also med density block. Concrete floor with wood finish porcelain tile. Rendered walls on the ground floor. Non-return valve fitted to foul sewer. Electrics set at 1200mm from ffl.

[Roger440]

6 hours ago, Mr Punter said:

We are in a flood zone and I have used brick and med density block cavity with Celotex CF5000 rigid insulation. Internal partitions also med density block. Concrete floor with wood finish porcelain tile. Rendered walls on the ground floor. Non-return valve fitted to foul sewer. Electrics set at 1200mm from ffl.

 

When you say rendered, do you mean inside or outside. Assuming outside, what did you do on the inside?

[scottishjohn]

On 27/02/2019 at 06:29, Oz07 said:

Looks good what kind of money per m2? Does this replace need for parge coating?

2 pack foam 

www.cfsnet.co.uk/cgi-bin/ss000002.pl?page=search&SS=2+part+expanding+foam+&PR=-1&TB=O&ACTION=.

Edited February 28, 2019 by scottishjohn

[Onoff]

7 hours ago, scottishjohn said:

2 pack foam 

www.cfsnet.co.uk/cgi-bin/ss000002.pl?page=search&SS=2+part+expanding+foam+&PR=-1&TB=O&ACTION=.

 

I've always wondered if you could "pour as you go" in a cavity wall with this stuff and not push the walls out?

 

Wish the dicks at Ford hadn't filled the lower rear comers of my Capris with it though!

[Mr Punter]

10 hours ago, Roger440 said:

 

When you say rendered, do you mean inside or outside. Assuming outside, what did you do on the inside?

 

Rendered inside, facing brickwork outside.

[scottishjohn]

2 hours ago, Onoff said:

 

I've always wondered if you could "pour as you go" in a cavity wall with this stuff and not push the walls out?

 

Wish the dicks at Ford hadn't filled the lower rear comers of my Capris with it though!

not if you do it in sensible amounts at a time --it will bond to itself  no problem --so mix it up run round the walls --make sure it does not hit the sides half way down ,or it could block it and leave a void  ,put in in layers.

I used to use it to strengthen moulds or as part of a mould if using a latex liner  for easy removal of grp moulding you wanted --I usedit to make old mini battery boxs --they were always rotting off  and to the back of moulds that you wanted not to distort -,like 3 piece wing moulds for old ford zodiac,. a bit that on the back of the grp mould before you remove from pattern -its then solid  and i mean solid ,really gets a proper skin 

[ADLIan]

Not a recognised method of insulating cavity walls and not BBA approved so would not comply with the Regs (north or south of the border). Injection of foam once the wall is complete is allowable but some of these systems are to cure wall tie failure and are not certified thermally - the completeinsulations.ie system referred to above falls into this category.

[Roger440]

2 hours ago, Mr Punter said:

 

Rendered inside, facing brickwork outside.

 

Interesting. This i assume is because its resistant to water unlike plaster?

 

I was going to do mine in lime, so after its got wet it can just dry out. Hadn't though of doing it this way. 

[Mr Punter]

21 hours ago, Mr Punter said:

Celotex CF5000 rigid insulation

 

This product has been withdrawn following the Grenfell Tower fire. The cavity wall product was not at fault but was part of a group of similar products, one of which was used as part of the failed cladding system, so Celotex withdrew the lot. Xtratherm do a similar product called CavityTherm, and it make no special claims as to fire resistance.

[ADLIan]

Celotex had also been overstating the thermal performance of this range of products!

[scottishjohn]

On 28/02/2019 at 11:39, MarkyP said:

I'm no expert on approaches to flood mitigation but thinking out loud I could see tea cosy approach being preferred over cavity. I think you would certainly want to avoid mineral wool in the cavity if there was a risk the cavity could be breached during a flood. The stuff takes an age to dry out once wetted (experience of dritherm32 batts left in the rain on my site) and when saturated tends to slump and deform. 

 

If going with EWI, then I would think an open cell insulation would be much preferred. EPS is open cell somewhat vapour open so in a flood the wall inside if wetted would be able to dry outward. Closed cell such as PIR or XPS I think would not allow this, you'd need to dry from the inside only. I think there are few system suppliers who specify closed cell EWI in any case. There were issues a while back with PIR boards used for EWI deforming once fixed, "pillowing" I think was the term used. Nearly all systems I considered were graphite enhanced EPS. There are some that offer wood fibre or mineral wool options but neither would be suitable where there was a risk of water immersion. I learned that EWI grade EPS differs from standard stuff. EWI grade it is cut from aged EPS blocks which are dimensionally stable. Standard EPS is not and there is a theoretical risk the boards could deform causing cracks.

 

 

I was not suggesting you fill entire wall with  it--just from base to above expected flood level ,as this indeed will be water proof --been used in yachts-canoes for years as buoyancy   and he was worried that eps sheets etc in cavity would allow water to get to inner layer

[Sjk]

On 26/02/2019 at 20:04, Roger440 said:

You can get cavity wall insulation that goes in as a liquid and then becomes, effectively expanding foam. Aside from some of the obvious advantages, it fully waterproof and ones of its claimed features is for use in flood prone houses. So it would be full fill and flood proof. Arguably, you could just do the 1st meter, then normal cavity insulation from thereup. Its expensive! https://www.completeinsulations.ie/spray-foam-cavity-wall-insulation/

 

Really liking the idea of this, will contact them for an idea of costs.

 

Would be good to hear from anyone who has used this method.

[Roger440]

16 hours ago, Sjk said:

 

Really liking the idea of this, will contact them for an idea of costs.

 

Would be good to hear from anyone who has used this method.

 

I investigated it some detail for retrofit in the cavity in my old house. Couldn't convince myself of any other system, especially has the bricks were rock hard, so much more likely that drivng rain would come through the mortar joints.

 

I seen to remember it was £8K to do the whole house up to the roof. The other spinoff was air tightness improvement on an old house. The worry i had though was where the joists went through the wall, there were gaps. Lots of them. Realistically, they would need filling/taping before doing it otherwise loads of the stuff would fill up under you floor! Much easier on a new house where that problem wont exist.

 

Ive toyed with doing it at my new please as there is a degree of flood risk, but the front half of the house is solid 9 inch wall, so probably wasting my time as that will fillup with water anyway!

 

Just going to concetrate on re-plastering with lime, so it can just dry out again.