goatcarrot

I’d need to put in extra long lintels I guess to accommodate the return

Normally with an extension I guess you’d use what was the exterior wall and just plaster to become internal. any reason (apart from cost) why I couldn’t just build another insulated wall next to the existing gable wall and then ensure continuity of insulation at the openings?

@pdf27 can I clarify it any further as I know it’s an unusual situation?! but yes basically that’s the idea. 3 bed now, deal done on that value, then improve later. I'm thinking of some form of infill panel in the outer leaf of external gable that can then be easily removed for continuity of insulation layer and blockwork tied in around it. Complex but there must be a creative way of achieving it

Thanks for the comments, very interesting and lots to think about. for various reasons we’re going with block and full-fill 300mm cavity insulation which, judging from the above, makes what I want to achieve more complicated but I’m going to try and figure out a way round it such as separating the two buildings with an entrance hall or somehow creating a way to tie in to the existing envelope. insulating at roof level is a good idea too and easier to ensure continuity.

Yes it’ll be substantial. I take your points but in this case it may be the lesser of two evils, just trying to weigh it all up at the moment, brain hurting! foundations, lintels, drainage and services all manageable, it’s the cold bridging aspect that I need to get my head round. Unless we had a thermal break like an entrance hall between the two buildings that separated the two thermal envelopes... any ideas comments welcome

@Conor twice as much really? it’s complicated due to the deal with my family for the land and me leaving the estate based on the value of the finished house now, it’s ironically in my interests to make it less valuable now and improve later if that makes sense. I know that makes it more difficult from a technical point of view as regards cold bridging but hopefully there’s a way it can be done?

Due to budget constraints we are thinking about building a 3 bed house now and then extending it when funds allow, with a sort of full height annexe. what design challenges does this present? the extension will be off the gable and I will over-spec the MVHR/UFH/ASHP now to cope with future demand. I’m wondering about how to tie-in the extension to what will be the existing building and extending the thermal envelope, foundation etc. obvious things include installing flashing now for extension roof abutting the gable and drainage/water supply etc. how else can I prepare things to minimise headaches later on?

Ok so that would sort the edges but what’s to stop them burrowing up from underneath I wonder. Can’t be nice chewing eps if you’re a rat I guess but I’ve seen evidence of it in an old caravan!

Thanks for the replies. I really like the raft idea however what about rodents nibbling away at the EPS , is that not a risk factor?

Did it dry out yet ie was it moisture from the plastering?

Depending on planning will accept it, I’m looking at charred timber cladding as I love the look of timber cladding but don’t want any maintenance issues or possibility of rot on the back of the boards after particularly damp spells. Probably to be used in smaller sections as a contrast to the glazing and stone/render. something like this https://permachar.co.uk/shop/ anyone used it and could give an opinion on performance/durability?

@ProDave interesting thank you if using strip footings with beam and block is it a similar approach but with the insulation on top? Is it then possible to achieve ph levels of insulation and thermal bridging do you know? I’m trying to look at alternatives to wood in the substructure

What attracts me about the raft apart from the simplicity is that I can potentially do most of it myself if it’s mainly just digging and moving stuff about. the stepped strip footings I can’t really envisage in my mind’s eye yet

@ToughButterCup thanks, ours is a big field with usually good conditions so we have space to get the muck away and even out the levels elsewhere avoiding trucking it out. quarry up the road does crushed stone for £15/ton delivered, maybe cheaper in bulk