Hamish Posted May 30, 2020 Share Posted May 30, 2020 Hello, I am new so apologies in advance if I accidentally do not follow protocol... I am looking for some help in "signing off" my plan for the foundations of a detached 6m x 4m SIP garden room workshop. The structure will use SIPs for walls and roof, which will also include some reinforcing steel in order to cater for a green roof using sedum roof tiles (65kg/sqm saturated weight). I wanted to go down the route of concrete raft due to clay soil and wanting to be belt-and-braces in satisfying a classification of being constructed of substantially non combustable materials...due to being sited < 1m from boundary fence. The structure will also be a woodworking shop with machinery installed. I also just like concrete. I should also note that I have already done the majority of sub grade excavations... One of the main questions I have is whether the intention to use a 7N dense concrete block mortared into a rebate in the concrete raft is a sound idea. Although I am using the room as a workshop, I wanted to make sure that future use could be various and as such I am trying to achieve a high grade of airtightness, soundproofing and insulation. For simplicity in the drawing I have left off the vapour barrier and house wrap, as well as internal battens + combo of cement fibreboard/ply and external battens + combo of cement fibre weatherboard + cedar cladding. Any pointers on where I have gone wrong or other suggestions will be greatly appreciated. Thanks for your interest. Link to comment Share on other sites More sharing options...
Onoff Posted May 30, 2020 Share Posted May 30, 2020 56 minutes ago, Hamish said: Any pointers on where I have gone wrong or other suggestions will be greatly appreciated. You have cold bridging there I think. Link to comment Share on other sites More sharing options...
dnb Posted May 30, 2020 Share Posted May 30, 2020 Make the perimiter foam taller, on the assumption there's a (battened) service void on the inside of the SIPS. This will minimise the cold bridge at the sole plate. You could of course opt to use something other than dense concrete, but then you need to be careful on anchor bolt selections. Link to comment Share on other sites More sharing options...
Hamish Posted May 30, 2020 Author Share Posted May 30, 2020 1 hour ago, Onoff said: You have cold bridging there I think. Thanks, can you point out where, what to change? Link to comment Share on other sites More sharing options...
Onoff Posted May 30, 2020 Share Posted May 30, 2020 14 minutes ago, Hamish said: Thanks, can you point out where, what to change? On these lines but I'm no expert. The cold bridge will be through the timber sole plate where the blue arrow is. @dnb suggests bringing up the perimeter foam higher. The foam gets lost in the service cavity. Cleverer people will be along shortly! Link to comment Share on other sites More sharing options...
dnb Posted May 31, 2020 Share Posted May 31, 2020 3 hours ago, Onoff said: The foam gets lost in the service cavity. Spot on. No expert on this either, but it's what my SIPS people have told me to do. Link to comment Share on other sites More sharing options...
Russell griffiths Posted May 31, 2020 Share Posted May 31, 2020 (edited) How do you plan on forming the step in the slab, that is a really awkward detail to hold the shuttering in place. Have you considered doing an insulated raft? with your electric heating in the screed, how will you put this in as you are laying the screed, it normally goes on top of the screed under your floor finish. The cold bridge is the diagonal line from outside to inside from your concrete blocks through to the perimeter insulation, increasing the perimeter insulation upwards will not fix this it’s just a small improvement, having 100mm insulation in the floor and just a thin perimeter insulation is allowing heat transfer at that junction. Edited May 31, 2020 by Russell griffiths Link to comment Share on other sites More sharing options...
Dreadnaught Posted May 31, 2020 Share Posted May 31, 2020 (edited) At the sole plate, for my timber frame we chose to split the sole plate in to a pair of battens, rather than a single piece of timber, so as to eliminate the cold bridge there. In my case I am having I-beam walls which will pumped full with cellulose insulation. (I'm having an insulated raft foundation.) Edited May 31, 2020 by Dreadnaught Link to comment Share on other sites More sharing options...
Onoff Posted May 31, 2020 Share Posted May 31, 2020 1 hour ago, Russell griffiths said: Have you considered doing an insulated raft? Like these details? https://www.isoquick.co.uk/timber-frame-sips Link to comment Share on other sites More sharing options...
Hamish Posted May 31, 2020 Author Share Posted May 31, 2020 Thanks for replies so far... 4 hours ago, Russell griffiths said: How do you plan on forming the step in the slab, that is a really awkward detail to hold the shuttering in place. I found this YouTube video that describes the process. Here is a screenshot from it: Certainly a bit of an effort but in of itself I think it should be achievable. 4 hours ago, Russell griffiths said: Have you considered doing an insulated raft? That was my original plan but as my site is in a terraced garden with no side access I am trying to reduce the amount of site excavations, which I am having to do by hand. So far I have not had much luck finding drawings for insulated raft without cold bridging problems that presents an affordable method with excavations kept to a minimum. The isoquick products that @Onoff point out look quality but the necessary excavations just seem overkill for a SIP garden room. Can you point me to any drawings that would a good suggestion? 4 hours ago, Russell griffiths said: with your electric heating in the screed, how will you put this in as you are laying the screed, it normally goes on top of the screed under your floor finish. I am intending to use the in-screed cable from Thermosphere, the suggestion on their site is that the cable can be stapled to foil facing insulation boards. I was then going to use a flow screed on top to be the floor finish. @Russell griffiths Is there any method that you are aware of to mitigate the cold bridge within the bounds of my general plan? Looking around other forums I did see one suggestion to use a course of Marmox thermoblock which the sole plate then sits on. However at £200 for 10 lineal meters this seems like an unreasonable expense for my small project. Link to comment Share on other sites More sharing options...
Russell griffiths Posted May 31, 2020 Share Posted May 31, 2020 (edited) sort of like this, but spend more than 30 seconds on it like I did to get it working right with dimensions etc. If your happy doing that shuttering then carry on I think you have it sorted. Regarding the cold bridge, you can put external XPS insulation, stuck onto the blockwork, this is then covered in something to protect it. You then alter your cladding battens to stick out further than the XPS. Edited May 31, 2020 by Russell griffiths 1 Link to comment Share on other sites More sharing options...
Cpd Posted May 31, 2020 Share Posted May 31, 2020 Spot on @Russell griffiths This would be my solution. Link to comment Share on other sites More sharing options...
Hamish Posted May 31, 2020 Author Share Posted May 31, 2020 Great many thanks @Russell griffiths Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now