Search the Community

Hi I wanted to put this in the rendering plastering trades section but couldn't click on that topic title for some reason. Has anyone rendered onto external polystyrene insulation? Its actually the base of my founds an EPS insulated raft. The two products i'm looking at are Aquabase EWI 226 a silicone render system with a fiberglass mesh or a cement slurry aquamat elastic with either 10cm polyestewr fleece or fiberglass mesh Anyone done this before and got any advice on either product or covered their EPS RAFT base in anything else that worked well? Cheers

I've finally got around to starting this blog. I'm hoping that it'll be easily updated and I'll provide lots of good pictures and info...we'll see how that goes. I'm at the point now where we have just taken our first big delivery, which is our insulated foundation system from Kore, this morning. So albeit, this process of building a house has been ongoing for some time, it has just become real that we are at the beginning of the build phase, which is very exciting. Some light background info - I've always wanted to build a house for the last 5-10 years, but it was a distant dream and wasn't quite sure how feasible it would be. I grew up in a rural house, my parents bought in 1983, modernised and updated over the years. It was a great childhood and spent many hours in the fields and in our garden, even just cutting the grass was fun (1 acre and a ride on mower). We sold that when I was 21 and ever since I've wanted to return to that life. I have two young kids of my own now and hence the want to return to the countryside to give them what I had was strong. I was always keen on building, swmbo, wasn't as such. So we searched and searched, but mostly the houses we could find that suited our needs were out of league (price!) and even if they were to be in our league there were things we would change or in the end it would be expensive to run. And hence that search helped my other half make the realisation that self build was our only option. My dad died in 2017 after a long illness with Dementia, a relief for him and for everyone else involved. We were very close and I took care of him day in and out, until he was in care. He was an engineer and had owned his own business since I was a child, albeit he lived a pretty simple life and was happy being at home in the garden he made and house he had renovated. Riding around on the ride on mower enjoying a quiet life...and now I guess that's exactly where I want to be. His passing left us with a little inheritance which has allowed this dream of self building to become a reality, I'm very thankful for this. I know it is something he would have been very excited to be part of and watch us do. So after messing around since 2017 and not being able to negotiate a plot or find one that was suitable (there's a lengthy thread on this!) I'd finally identified 4 acres in July 2019. It took a bit of time ( I had to confirm services and remove an Agricultural tie) but completed purchase in Jan 2020. I'll not cover the planning process in detail, but the plot had legacy planning permission which was 24 years old, but at that time the development had commenced and hence it was a straightforward change and submission of our designs. Building warrant was granted a week ago, with very little hassle really. I joined Buildhub in September 2019 or thereabouts. It's been a wealth of information that has helped me shape the design of the house and provided no end of guidance which I am very thankful for. It has allowed me to validate my opinions and approaches and learn from others to ensure i am following the right path. I started out prior to buildhub wanting a SIPS house, in fact googling that may have made me find my way here. Quickly I decided I wanted an insulated foundation too, I went around in circles a little bit with both of these decisions and reading others opinions on here. I even thought at one point they would both be too expensive for me , however I sit here writing this first post having taken delivery of my insulated foundation today and my SIPS kit is on order and due sometime in February. I don't actually need the insulated foundation till mid-late January but made a decision to get it in the country before Brexit issues occur and tariffs are possibly applied in January (rumoured at 6%). I'm very glad I made that decision as today our new strain of COVID has caused everyone to close the doors to us here in the UK, another couple of days and god knows when I would have gotten it. There is lots of other decisions and stuff has gone on in the background with planning and mortgages and budgets to get here, but that is mostly done and hence I feel this is the end of the beginning and now we can enter the start of the middle.... I'm very pleased and excited for the road ahead. I like pictures in blogs....here's a few of the Insulated foundation delivery today. Stored at a friends farm for the time being. It's being stored outside, has a few tractor tyres on it now to stop it blowing away and the main pallets are all strapped down. That's me standing on top.......

I'm rapidly approaching starting work on site. Civils mate who is doing groundworks called yesterday to say he could start next week if I wanted, but I haven;'t yet engineered the life out my drainage and levels and hence I am not quite prepared. I've a large flat plot, and using Treatment plant and a direct discharge into a burn (SEPA approved). I'd deliberately set the house 'into the' ground rather than on it, so that it looked natural rather than sitting on top of the ground, and also to avoid excessive extra infill material if I raised it up. However this leavesme limited amount if space from FFL to the normal water level in the burn, approx 1.25m. I am following the popular Kore foundation system route and expecting that I need to drop all drainage out through the bottom, rather than put sewage pipes out walls. The issue I have is that I am struggling to get the fall required and also protect against backflow from the burn. Normally the burn is only 50mm deep, but when there is heavy rainfall and storms it can rise 1m. The distance from the drainage through the slab to the TP is 45m, and this is where i am struggling to achieve the minimum 80:1 fall on the sewage outlet. See diagram below, some buildup notes Depth of Kore system - approx 400mm Hadcore and sand blinding: 250mm From here, I have guessed that I can leave the drainage pipe 50mm below the underside of the hardcore. Now using a GRAF one 2clean (It'll be that or equivalent, biopure, etc). From where the septic tank is to be sited, I drop it 675 below surface (535 + 140), I f i assume that the drainage pipe top is 50mm clear below the bottom of hardcore, and it's a 110mm pipe. Then that means the fall height is 465mm (625-160) which is over 45m giving a ratio of 96:1, which is a good shallower than it needs to be. Second issue being, even with the TP being as high as possible here, during storms I will backflow the tank. I think this can easily be dealt with using a backflow device (picture below) the water usually comes down within a few hours - however I suppose it could stay up for a day if we had a prolonged period of rain (I'm on the west coast of Scotland - so highly likely). Now possible solution is to drop the tank down further 200mm - which would give a much more reasonable (465+200= 665 fall height) 67:1 over the 45m. However now I'm very close to the water level (205mm) constantly and regularly it would come up above the outfall. I was trying to make sense of the best route here by asking - but in writing this thread I think I have answered my own question. It would seem that the best plan is to drop the Tank down the extra 200mm and then just changed it from a gravity type to a pumped solution, then this all goes away? or do I do somethign different and pop the waster out the wall - which won't seem to be an elegant solution? In either case I'll need a backflow device, regardless for peace of mind. I've attached the site plan and foundation plan for reference. Apologies it might be a little disjointed and hard to follow...I've been rattling this around in my dreams all last night and needed to put it on paper to work it through. 724-11 Site Plan.pdf 724-13 Foundation Plan.pdf

For those with an insulated raft foundation, what was your ground bearing capacity figure? And was your raft designed with extra thickening? My SE had made noises that my ground bearing figure of 50kN/M2 is a bit low but workable. His latest design of the raft has 25% of the area thickened to 400mm and in these areas insulation reduced from 300mm to 150mm. This feels like a big step down in thermal performance to me, but perhaps I shouldn't be so concerned. During the ground investigation I was told that I had ideal ground for a raft so not sure how a 50kN/M2 figure has been derived. I've asked the GI chap if he could revisit his Standard Penetration test results with hope to increasing the ground bearing figure; no response yet. I also feel the SE is being over cautious; he has the slab edge thickened where a single story porch will be. That seems really unnecessary.