Browse Forums Paving & Concreting 1 Jul 24, 2012 6:52 pm hi i'm thinking of adding 150mm wool around the house(to get a 0,21 U number) and later lay bricks around that to get a durable finish, but i probably need to expand the foundation a bit to hold all that weight.... i havent calculated the exact overlapping thickness yet, but is it even possible to expand the foundation with new concrete and rebars? the house is like 9x11m wide and current foundation goes ~2,5meters into the ground, counting from the wood layer. i was thinking of adding maybe like half of that length (option 1 on the picture) or maybe even start from the middle of the cellar windows(option 2.). here's the pic: http://img6.imagebanana.com/img/5coti3z7/conc.jpg orange color represents new additions... if it is possible, then how deep should it be and how to attach the rebar? i also need to insulate the foundation with some polystyrene foam plates...(didn't add those onto the pic) thanks Re: how to expand concrete? 2Jul 24, 2012 7:34 pm Should of though of this when you laid the slab I wouldn't add to the slab thickness. The bricks walls are a large weight and no matter how well you attach the new slab to the old, it will always be a weak point. You can get something like Air-cell Insulbreak 80 that together with your brick wall gives a U value of about 0.45 (R=2.2), which is pretty good. If your inside wall is also brick then you get thermal mass on the inside which assists the insulation for a passively heated and cooled house. More insulation may be useless since windows have a U-value of 5 at best and even if they occupy only 10% of the outside wall area, you'll lose more heat from the windows than R2.2 walls. Any reason for such extraordinarily high wall insulation? Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: how to expand concrete? 3Jul 24, 2012 8:01 pm high wall insulation as the low number? i'm thinking of adding a central floor heating too, so every little helps... the walls are wooden logs(from the 60s), which should be ~u0,54... there's also a brick layer atm, but dunno how much that gives in addition. if the winter is like -25, you can feel the wind coming in from the window racks... and sucking itself in from the floors... btw, the current concrete is not smooth, so the new layer could hold itself in place from there too? maybe even add 1 or 2cm wide metal rods into the wall and weld the rebar onto that? dunno what the cost would be tho... maybe just cheaper to pour the whole length then? Re: how to expand concrete? 6Jul 25, 2012 9:10 pm Although more insulation is always better, there comes a time when there's very little benefit. Consider the case of 90% walls at U = 0.50 and 10% windows at U = 3.00 (a good double glazed window). You're overall U value is 0.75 (That is, R = 1.33 W/m2.K). Now if we increase the walls to a U = 0.20, then the overall U is 0.48 (That is, R = 2.1 W/m2.K). So, you've increased your wall insulation 2.5 times, but reduced your heat loss by only one-third. If you really want to increase your wall insulation, can I suggest you hang the external cladding off your existing external wall. This way the bearing load will be on your existing slab. Cheaper and stronger. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: how to expand concrete? 7Jul 25, 2012 9:49 pm If I get this correct, you need maximum insulation in the walls. I would suggest 150mm polystyrene sheeting applied over the stud wall and then rendered or a brick wall on a separate footing tied to the stud wall then rendered or coated. I think you will find this better than any wool or similar product. 100mm thick poly and render gives in the region of R4.0. That is a serious cold temperature, and the roof insulation should be dealt with as well to the most affordable way. Settlement 1/2/12 New Shed 23/3/12 Slab poured 27/3/12 Frame complete 4/5/12 Roof complete 1/6/12 LOCKUP 29/6/12 Our new build blog http://kareenhillsownerbuild.blogspot.com/ Re: how to expand concrete? 8Jul 26, 2012 5:59 pm how did you calculate U with different percentages?:p i'm thinking of getting new windows too because current ones have too much framing and one of their middle beam runs exactly on eye level :s:s The new ones would have to be double or triple glazing with u1.4-0.8. Some krypton filled windows are even u0.6 with e5%... i probably dont want to know how much they cost tho... poly-foam is not recommended to use with logs because of their different humidity flow or whatever... i would have to use rock wool. i could hang some wooden cladding off the existing wall, but it probably won't hold the brick? don't like to use wood because that's too difficult to maintain... i'm also thinking of removing the whole 2nd floor(1st floor is the ground floor here) and build it up again from scratch because the current build is done with thick planks covering both sides of the walls and it probably weighs like 20 tonnes :d The roof has also thick and heavy beams with old asbestos sheets... and there are also 2 dormers on 2 sides, which i dont like at all... Re: how to expand concrete? 9Jul 26, 2012 9:47 pm To work out the U value for different percentages, just multiply the individual U values by the percentage (for example 10% = 0.1) and add them all together. The new U value is the combined U value for the entire surface. For the example given, U(total) = 0.50*0.9 + 3.00*0.1 = 0.75 Please note the units for U are W/m2.K and R is the inverse, m2.K/W. (The units for R I gave previously were actually the units for U - but who looks at units!) By the time you remove the entire 2nd floor, replace the windows on the ground floor and add new external walls on the ground floor, you might as well knock down the lot and start fresh and build exactly what you want. It would have to be cheaper - certainly would be in Sydney. Demolition August 2009, Construction Started September 2009, Completed December 2010 To my understanding early saw cuts are to control shrinkage cracks, so doing them now would be pointless. Control joints may reduce ugly cracking during periods of soil… 3 9863 Hi all I need a guidance on how far I need to space expansion joints in the concrete driveway and its type (keyway/foam.) Contraction joints are at 3m max for a 125 slab. 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