Modern solid wall construction

[Archer]

Just thought that I'd share some learning for others who are interested in looking at this form of construction. 

 

I was investigating external solid wall construction using Celcon Solar aircrete blocks for our single storey extension as a way of keeping cost and wall thickness down. We were looking at "thin joint" to improve airtightness, weathertightness and reduce coldbridging (you can also use with conventional 10mm mortar).  Some thoughts and constraints; 

 

1. Passage of moisture - In London which is classed as sheltered in the driving wind index you can in theory specify a solid external wall as thin as 90mm and be compliant with the regulations. There are other considerations (below) and if you are building in more exposed parts of the country this increases significantly. This is backed up in the BBA certificate which explains the principles - essentially that a water-resistant render or cladding is used, and that the blocks have a relatively high water and vapour resistance. Roof to be correctly detailed with overhangs etc. 

 

2. Structure - Solar blocks are only suitable for lighter loads but there are other stronger, denser blocks available. A key design constraint is in Part A - minimum wall thicknesses.This states that residential buildings under 3 storeys using this form of construction must have a wall that is a minimum of 190mm or 1/16 of total height (whichever is greater). In practice this means using 215mm blocks in most cases or possibly 200mm for flat roof / mono-pitch construction. You can go thinner with structural engineers calcs if this works or by using piers. 

 

3. Acoustics / Noise - Although it would appear to be a good option acoustically (thick wall with reasonable mass) there don't appear to be any robust details for this type of construction which means making the case to your building inspector / officer or employing an acoustician. There are details available for party walls which comply. Maybe someone can correct on this? 

 

4. Thermal - You can achieve compliance with the current regulations (for an extension - 0.28)  by using the following wall build up from in to out - wet plaster, 215mm solar block, 60mm Sto insulated render system (other brands available!) consisting of 50mm PIR with 10mm silicon render mechanically fixed on rails to the wall. Total wall build up c. 290mm

 

I'd be interested if anyone has experience of the cost of this compared to other options? Instinctively you'd think pretty good as it uses familiar trades and products whilst reducing labour against cavity wall construction. 

[PeterW]

13 minutes ago, Archer said:

. Thermal - You can achieve compliance with the current regulations (for an extension - 0.28)  by using the following wall build up from in to out - wet plaster, 215mm solar block, 60mm Sto insulated render system (other brands available!) consisting of 50mm PIR with 10mm silicon render mechanically fixed on rails to the wall. Total wall build up c. 290mm

 

I'd double the insulation on that - you will not notice the extra 50mm in thickness but will notice it in reduction of heating bills !

 

Thin joint has been around for a while but you may struggle to find a builder who can use it

[Declan52]

Why not just build a 100 mm standard block on the outside then 150mm cavity with beads blown in then another 100mm  block on the inside. To boost your thermal properties you can go with a thermal block here.

Will be cheaper and much easier to build.

How much are solar blocks compared to standard or thermal blocks??

[ProDave]

Why block at all if rendering?

 

I am achieving a U value of 0.14 in a well insulated timber frame with wood fibre board for external insulation and render applied to that. Overall wall thickness inside to out of 360mm including a service void on the inside for cables then plasterboard.

[Ian]

@archer

if you are interested in a solid wall construction have you seen the range of insulated clay blocks by Porotherm?

http://clay-wienerberger.com/expertise/our-latest-developments-1366178159710

[Archer]

4 hours ago, PeterW said:

 

I'd double the insulation on that - you will not notice the extra 50mm in thickness but will notice it in reduction of heating bills !

 

Thin joint has been around for a while but you may struggle to find a builder who can use it

 

It really pains me to build "just to Building Regs" but it is 3 sides - 3m x 4m added to an existing 1930's solid brick wall property. Therefore it won't give much advantage to be really well insulated whereas losing 15cm of room space in London is a real premium

 

3 hours ago, Declan52 said:

Why not just build a 100 mm standard block on the outside then 150mm cavity with beads blown in then another 100mm  block on the inside. To boost your thermal properties you can go with a thermal block here.

Will be cheaper and much easier to build.

How much are solar blocks compared to standard or thermal blocks??

 

Same answer as before - although this build-up has better thermal properties it is also approx 60mm thicker... the cost question I don't know the answer too. I read elsewhere that solid block with EWI is more expensive than cavity construction but we are considering a decent silicon render anyway so not sure if this would be the case. We also wouldn't be able to use mineral wool because we are in a floodplane so closed cell insulation is needed.

 

3 hours ago, ProDave said:

Why block at all if rendering?

 

I am achieving a U value of 0.14 in a well insulated timber frame with wood fibre board for external insulation and render applied to that. Overall wall thickness inside to out of 360mm including a service void on the inside for cables then plasterboard.

 

Absolutely - this is the question. Looking at this has been a bit of a last resort because of issues thown up by our flood risk assessment (Zone 2). We are currently comparing mgo / fibre cement faced SIPS against this type of masonry construction. Traditional timber frame could also be an option. Has to be flood resistant / easily repairable though so no luck with mineral wool, wood fibre etc. OSB seems to be out according to current guidance although SIPA and Kingspan Tek both feel it is suitable 

[Archer]

3 hours ago, Ian said:

@archer

if you are interested in a solid wall construction have you seen the range of insulated clay blocks by Porotherm?

http://clay-wienerberger.com/expertise/our-latest-developments-1366178159710

 

Love the look of Porotherm Ian, in fact if I was building a house this might well be what I went for... however I don't know if it makes sense for a small extension - not "tried and tested enough" for local builders to price competitively and no off-site companies which produce it. 

[Mr Punter]

How about 100mm rendered block, 100mm cavity with Celotex CF5000, 100mm block or lightweight block?  This is good for flood resilience and not bad for SAP calcs.

[Archer]

49 minutes ago, Mr Punter said:

How about 100mm rendered block, 100mm cavity with Celotex CF5000, 100mm block or lightweight block?  This is good for flood resilience and not bad for SAP calcs.

 

That's very interesting. I wasn't aware that you could fully fill the cavity with foam insulation. Your suggestion has lead me to a similar product - Xtratherm full fill which is available in 75mm width's to achieve up to 0.25 U value. This would bring the overall wall thickness roughly in line with the single leaf EWI option above. Might be a good option if builders prefer quoting on cavity construction.  

[Declan52]

I used full fill cavity boards on my build but I done it myself so made sure every board was installed properly. That's why I mentioned beads. They get blown in and the cavity gets filled up with no issues. If you leave gaps using cavity boards then you get cold spots on the wall. 

How high of a risk is flooding???

[Mr Punter]

3 hours ago, Declan52 said:

I used full fill cavity boards on my build but I done it myself so made sure every board was installed properly. That's why I mentioned beads. They get blown in and the cavity gets filled up with no issues. If you leave gaps using cavity boards then you get cold spots on the wall. 

How high of a risk is flooding???

 

Yes, you need to watch the install like a hawk and I suspect that only those like Declan know this.  I was fairly vigilant but with 8 sub contract bricklayers who changed each day it was impossible to even get the boards fitted the right way up most of the time and if they were called on it they were incredulous.

[Archer]

3 hours ago, Declan52 said:

I used full fill cavity boards on my build but I done it myself so made sure every board was installed properly. That's why I mentioned beads. They get blown in and the cavity gets filled up with no issues. If you leave gaps using cavity boards then you get cold spots on the wall. 

How high of a risk is flooding???

 

Sorry, I obviously wasn't properly engaging on your previous post - so presumably with EPS beads you could adjust the width of the cavity to suit the required U value. It's essentially the method they use on retro-fit cavity wall insulation (Green deal type work). I guess that you would need a sub-contractor to because my understanding is that the beads are mixed with an adhesive as they are blown in. Not sure if that would be cost effective on such a small project but to be honest I've no idea, might be worth investigating. I hadn't thought about quality control - instinctively the single skin with EWI seems like it might be harder to get wrong because the final render coat goes directly on the insulation so any gaps should be pretty apparent. I might be way off on that though.

 

The risk of flooding is negligible in my view but the planners are quite concerned - to the extent that the flood risk assessment is the only planning condition we have. Site is listed in flood zone two with between a 1 in 100 and 1 in 1000 chance of flooding in any given year. I'm trying to establish the datum height for these flood levels as are finished floor level is already about 30cm off the ground.

[MAB]

For info my recent extension in South London was built with 215mm thick Celcon Solar solid block work walls, external face 20mm smooth render, internal face 25mm treated batterns plus 60mm thk Gyproc Thermaline Plasterboard & skim to meet current Building Regs.

[Ferdinand]

@Archer

 

Quote

That's very interesting. I wasn't aware that you could fully fill the cavity with foam insulation. Your suggestion has lead me to a similar product - Xtratherm full fill which is available in 75mm width's to achieve up to 0.25 U value. This would bring the overall wall thickness roughly in line with the single leaf EWI option above. Might be a good option if builders prefer quoting on cavity construction.  

 

If you get your insulation from say Seconds and Co (they get the Kingspan not quite perfect stuff), then you could get it well below half price (I recently paid approx £10 a sheet for a pallet of 50mm PIR 8x4s, delivered) - so the extra materials will cost you the same as the half-amount via a normal channel. I bought a shed to store it and the rest in which I will reuse elsewhere later.

 

You just need somewhere to store it, and to watch the site for the correct stuff. Can save thousands if you do it with other materials too.

F

Edited August 17, 2017 by Ferdinand

[Archer]

6 hours ago, MAB said:

For info my recent extension in South London was built with 215mm thick Celcon Solar solid block work walls, external face 20mm smooth render, internal face 25mm treated batterns plus 60mm thk Gyproc Thermaline Plasterboard & skim to meet current Building Regs.

 

MAB - Thanks for posting, can you provide any further information on why this system was chosen (was it cost effective for example)? Just a couple of thoughts that I had - why did you decide to insulate internally rather than externally? Did you or your builder use thin joint?

 

Final question was whether you had any issues with Part E (resistance to the passage of sound)? I can't work out if I am interpreting the regs wrong, but Celcon haven't been able to give an acoustic detail for an external wall (not sure if these are even needed). 

[MAB]

The solid block walls were quicker to errect and also easier to lay, (I'm not a bricklayer but when I was younger I built my own study/garage extension walls with them!), only seen thin joint used on commercial buildings, domestic builders don't like them I think, as more difficult to compensate for variations in levels and plumb by varying joint thickness, etc.

With internal insulation on batterns you get a small cavity (dot & dab is alternative maybe?) and need to allow for where you might fix heavy items later like radiators with extra timber batterns and then record with photos before the batterns are covered over by the themal plasterboard! All external walls and no issues with passage of sound in my case.

 

U-value tables for solid walls (Celcon /Thermalite, etc) and req'd insulation are given by many local councils, see here and scroll down:-

http://www.haringey.gov.uk/sites/haringeygovuk/files/u-value_guidance_nov_06a.pdf

Edited August 17, 2017 by MAB

[Mr Punter]

7 hours ago, Archer said:

Final question was whether you had any issues with Part E (resistance to the passage of sound)? I can't work out if I am interpreting the regs wrong, but Celcon haven't been able to give an acoustic detail for an external wall (not sure if these are even needed). 

 

Part E is mostly for flats and terrace housing.  Not applicable for you.

[Archer]

6 hours ago, Mr Punter said:

 

Part E is mostly for flats and terrace housing.  Not applicable for you.

 

Thanks for this advice - I thought that I was going crazy because reading through it all seemed to apply to separating walls with occupants on the other side. So non-separating external walls don't have to demonstrate a minimum standard

[jayroc2k]

I recently completed a 6m by 5m extension to an end of terrace house, I put in 100mm celotex in the old and new sections floors, front room of the old house with 50mm pir boards, only one side wall of about 7m is still uninsulated original brick. 

 

result? Disappointed.

I did not live in the house before the build so can only compare it to the newbuild SAP B flat I moved from. That flat stays warm until January at the very least while I am already using heating in the house in September. 

 

Still feels draughty. All new double glaze sash windows, 2 bedrooms out of 4 fully insulated internally but not warm in September!!

 

so don't go crazy on the extension, it will make wry little difference due to the rear of the house

 

I used full fill mineral wool for the cavity as I did not trust the builders to use celotex without gaps.