Archer

I looked at something similar to this for our extension and I believe you are able to build a single skin block wall with an insulated render or brick slip carry system. There are rules around the slenderness of masonry walls so you need to use a 215 block I think. As for cost, not sure to be honest. Brick slips can be more expensive than brickwork. On the other hand you would get a thinner wall build up and less potential quality issues with the cavity / insulation continuity. You can have the brick slip panels prefabricated off-site as well though this may increase cost. Plenty of contractors and developers use something similar but mostly for retro-fit work.

Just to add some benefits of smart meters for the sake of balance - they enable remote meter reading which cuts down the likelihood of errors, especially for more vulnerable people who won't spot the mistake; they allow people to see how much energy they have used and to tailor consumption accordingly; it's a tool to help change behaviour and to enable consumers to save money and understand energy usage; more than anything the smart meter roll-out is helping towards energy efficiency and so climate change. The current generation may not be perfect but there are significant benefits in a national roll-out and even more so in older houses where landlords or owners have already insulated the loft and won't consider more radical measures. My experience is that (when they work) they do succeed in getting people to save energy. My Mum is paranoid about her smart meter, measures out the amount of water in the kettle before putting it on. On the older district heating schemes there were no heating controls for individual flats and the result is people leaving radiators on all the time, even in summer. Sorry if this is a little off-topic from the OP, but lots of people read this forum and it would be a shame if they were put off smart meter installations.

Belt and braces would be to locate a VCL behind the insulated plasterboard, but manufacturers seem to accept that the integrated VCL provides enough protection without further sealing. 2 coats of Gyproc Drywall Sealer provides vapour resistance to the plasterboard when it is edge sealed with sealant or foam.

Thanks for all of the responses. I definitely haven't ruled out instructing our architect because there will be a number of drawings needed and I don't have the skills - question is whether I would trust a builder to do it... maybe. The modular extension / garden room companies actually have excellent in-house design teams but our project seems to be a little more complex than most are interested in. Getting a BCO and a structural engineer appointed seems to be the logical next steps and then I'll make a final decision on whether we can do it on notice or by a full plans application. Peter - we are building on the outskirts of London (£££...) Where is your approved inspector based? Jeremy - I am mega impressed with your construction details. Do you have a design background or were you using a software package to produce them?

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

Good idea having a practice run first so to speak. Is your architect appointed to be a contract administrator as well? This is a separate service from design (a form of project management) and most professionals would charge significant fees. In return you should get regular, managed site meetings and an element of quality control and sign off on the payments. Depending on your trust in the builder you may not feel that you need this level of service on £15k of works.

That's very good advice from Ferdinand - especially around prioritising good ventilation and acoustics - get those two right and you knock out 50% of complaints straight away. Allowing pets is more of a gamble, fine with considerate owners but I've seen some horror houses chewed up by dogs as well (plus neighbour considerations etc).

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).

They are not hard but the terminology can be a little daunting to begin with. JCT Homeowner Contract 2016 could be a good starting point for you. For smaller projects there is always going to be a balance between how far you go with due diligence - sounds like you already have a professional architect on board which is a good first step. Having a detailed scope of work, accurate drawings and a simple contract (which includes payment terms) are all useful ways of protecting yourself. Common sense and human decency go a long way as well in my experience. For larger, more complex projects we would look at things like contractor solvency, references, insurance (site, public liability etc), performance bonds and retention. This is likely overkill for your proposals and I am finding the same on my extension - the risk is spending more on professional fees as a percentage of work than you get back in value. If you are interested in further reading then the RICS Construction Project Managers Pocket Book is very comprehensive, alternatively Mark Brinkley's "House builders Bible" is a great accessible read.

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.

Welcome Mike. Good luck in finding a plot, signing up for local self build register's where you want to live could be a good first step

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.

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.

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 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. 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

Be careful if you are thinking of selling the house in the near future. It's unlikely to get picked up but...

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.

Also - Love the cartoons!!

Approved Inspector vs LABC is something that I am still contemplating to be honest. Was hoping to receive a magical recommendation from either our architect or modular company so am still having those discussions now. The one that is worrying me a little bit is means of escape and fire - because we are essentially proposing a three storey flat with an open plan kitchen to the ground floor. We may need an auto-mist system and I am hoping there can be some lenience on things like inner rooms definitions, and the size of escape windows. It all feels quite chicken and egg - like you can't decide X until you understand Y - in our case the building control officer almost feels like they will be a member of the design team, but we need to resolve who is appointing them first. Anyway, thanks for the advice above - I feel like it is getting a little clearer in my mind now. We have one detailed quote in with two more builders round today. After I've met them we'll decide whether the extra help of the architect is worth paying for (I guess it comes down to cost and how much confidence we have in the builder). If we go design and build then I will put together a written specification myself and ask for a contract.

Thanks, that's a good suggestion. I hadn't thought about a building notice. I do wonder a little bit if I'm making it harder than it needs to be by trying to save some design fees, but then the saving seems quite tempting as well.

Hello Folks, advice needed from the wise heads on this forum... So I am in a bit of a quandary about the best way to proceed with the next bit of our project having secured planning permission. We are doing a small (but expensive / complex) extension which will house our newly located kitchen when its all complete. Our architect, who has been good, quoted in two parts - for planning drawings and then for the building control process and drawings. Cost of this second set of drawings is around £1500 excluding structural engineering calcs and BC fees. Separately we have been talking to providers of modular extensions - SIPS providers and garden room / TF providers. This appeals to us because we can get most of the construction work for the extension including foundations completed really quickly. They mostly include 10 year insurance backed warranties and can fully erect the extension in 2 weeks. We've got around 3 outline quotes from these sort of companies and they feel like they are in the right sort of ballpark... however a couple of them are not interested in doing the wider re-modelling works that we would need. They have priced off planning drawing which lack detail although the quotes returned have been quite comprehensive. So if were to proceed down this route as a straight design and build appointment we would need to look at getting at least one follow on contractor in; This work would include connecting the soil pipe to a neighbors property, demolishing a porch, knocking through an internal wall, moving a radiator, adding a roof light, finishing the floors and installing the kitchen. So quite a lot. The architect has currently allowed for brick and block construction - it looks like SIPS can give us around an extra 30 cm of room (on a 3 x 4m ext). He is happy to draw them up in SIPS but hasn't really worked with them before. His design work will almost certainly be more expensive than getting the contractor / supplier to undertake it. Money is really tight so... what I have been wrestling with is whether you get better value by pushing on with the architect - getting detailed drawings and a specification which lots of builders can then fully price off. Or alternatively, should we take a significant saving on design and push ahead with a modular company for the main extension and then separately get quotes from builders for the follow on work? Phew, that's a long email about design and build vs tendering fully detailed drawings. Help needed!

Thanks Jack, that's useful - when you look into it on the internet it seems that quality control has been an issue for the MGO board industry and is one of the factors preventing adoption becoming more widespread. On the face of it, its something of a wonder material even having strong sustainable credentials. There are a few suppliers who are quite meticulous about where they source the boards to avoid issues that have been experienced in the past. If we proceed down this route, we would certainly be asking for that information - and also the supplier would be erecting and assembling which should remove some of the risk, at least initially.

I think this may have been done elsewhere, but any views or experiences with metal Decra / Metro-tiles? Considering as an option for our extension... they are quite common on conservatories - just wondering if it would look a bit naff compared to normal plain tiles when up or if it would be difficult to notice the difference? Also how expensive are they - look like they would be quicker to install or DIY even.

Hi Ben, I'm in the process of scoping SIPS for a smallish extension project in London. Interestingly, we also looked at some of the alternatives others have mentioned here including Durisol which I was quite keen on but they never returned my emails. One of the key considerations for us was wall thickness and it looks like we can shave up to 90mm off each wall by using SIPS which would be quite considerable on our project. In terms of your questions, a 4th option you could consider is one of the SIPS manufacturers that allow render to be applied straight to the exterior face of the SIPS panel. To achieve this the exterior sheathing board of the panel needs to be either cement board or MGO board - both of which are slightly more expensive than OSB SIPS but have other advantages - ie. they are fireproof, vermin proof and unaffected by moisture rot. I was slightly suspect as to whether this system was building in a future weather-tightness issue but managed to track down a BBA certificate for a provider using this system ("Panablok 100 preformed structural wall") and it was ok'd for 60 year design life. Looks like the certificate has been taken off the BBA website now. If you accept that the risk should be low because both cement board and PUR foam are essentially waterproof then this option would save you cost and wall thickness (suppliers like Mantle and others are still encouraging it). Weighing up the merits of cement board and render vs block and render. In my mind; Cement board - supported from walls so may reduce foundations and cost; reduced materials and storage; reduced wall width Block - may have be more durable in the (very) long term because its self-supported; better acoustic separation; slight thermal benefit (easily outweighed by adding insulation); may help reduce overheating by adding thermal mass

Should have added Jack - no Right to Light issues. Good thing too because that would be hugely costly and a definite scheme killer

Hello all, Thanks for your advice and knowledge as always. Jack, that's interesting, I hadn't realised that to be honest although it makes sense. We won't actually be taking any daylight or "visible sky component" (VSC) either because the extension side wall is the same size as the existing fence and then pitches up towards the roof ridge line at 45 degrees. The neighbour is ok with it and has been incredibly accommodating, even allowing us to block up an airbrick to the bedroom. Anyway, long story short - the planners seem to have accepted our application with no changes! Very pleased. We haven't got the final written confirmation yet but it seems they were mainly concerned about the extension height we have addressed by illustrating the 45 degree line and keeping to a max 3m width out from the existing building. They seemed happy enough with this, possibly because other maisonettes on the road have had similar work done (London...) So good news - crashing on with a bunch of other issues now in what must be the most fiddly 3m extension possible. Other items we are progressing; purchasing our freehold to consent works; party wall; fire strategy for open plan 3 storey building; flood plane issues (SIPS are not recommended - looking at MGO over OSB for sheathing board...).