Insulated concrete slab for workshop

[gaz1]

i will also give you this one as you use less concrete but still have good strength the second pic used in garages


we use stretching the steel wire so it bows but we can use steel mesh

this ones area hits -20 degrees in winter

a rocket stove can heat this or as ive posted on the forums can run this

 

[DecK]

If you have thermal blocks there use a course at the floor insulation interface with the wall

 

[knighty]

I've always seen concrete -> insulation -> concrete

never just insulation on top of the hardcore.... is that the normal way now?

 

[DecK]

You only need concrete under the insulation layer if you need a structural floor slab if your incorporating U/F heating in a screed on top of the insulation layer. Screed for U/F is going to be 75mm at most with concrete. Less with an anhydrite screed. OP hasn't said he's going with U/F heating. Design above is how I'd go about it. The thermal block at insulation/floor level is just an extra thermal break. Pretty much the same as what he posted earlier

 

[gaz1]

you have to take there area in as well its not like uk or ireland its cold in there area

colder hasher climates need different things

 

[DecK]

Possibly, but the OP asked how to eliminate the cold bridge at the floor/wall interface. Thats what I answered

 

[8ob]

All sounds a bit too complicated and expensive for very little gain, I would spend the money ramping up the insulation elswhere.

Bob

 

[Morrisman]

aha, so basically I'd pour footings / normal strip foundations first, then build walls (at least up to floor level), and then pour the flor slab afterwards?

When I built mine I dug footings, poured concrete, then built two layers of 6" solid concrete blocks to what would be floor level. That was backfilled, hammered down then a DPM laid in. I never bothered with insulation but I could have left some of the rubble out and put a good few of polystyrene in at this point then concrete over that. And I could have put a layer around the edges, effectively insulting the concrete slab totally.

The DPM then folded over the walls and became the damp proof course. I then built up in 4" concrete blocks.

 

[knighty]

for the cold bridge where floor meets the wall, I've always seen the floor stop short of the wall and insulation on the walls going down and meeting the under floor insulaton

but.... where I've seen it done it's when a floor has been dug up and insulated, not a new build

 

[Henrik]

Thank you everyone for all the replies! Much food for thought


I should clarify I actually live in south east England just inside the m25, but originally from Sweden.

I like the thermal brick idea with the extra lining between the floor slab and wall because it seems achievable with reasonable diy skills and the manpower I have available - I think I’ll probably build something like that.

As for if it’s worth it, I want the “reasonable best” I can afford and am able to build. I’ve always had terrible workshops and garages here, with bouncy floors, damp etc etc. I want something where the lathe won’t rust, and where I can passively heat as much as possible etc.

Will post a thread in projects when I have some photos to show.

 

[Gareth J]

Thank you everyone for all the replies! Much food for thought


I should clarify I actually live in south east England just inside the m25, but originally from Sweden.

I like the thermal brick idea with the extra lining between the floor slab and wall because it seems achievable with reasonable diy skills and the manpower I have available - I think I’ll probably build something like that.

As for if it’s worth it, I want the “reasonable best” I can afford and am able to build. I’ve always had terrible workshops and garages here, with bouncy floors, damp etc etc. I want something where the lathe won’t rust, and where I can passively heat as much as possible etc.

Will post a thread in projects when I have some photos to show.

You can get special, thermally insulating, yet structural, blocks for doing just this thing. "Foamglas" or similar:
https://perinsul.foamglas.com/en-gb/thermal-bridging-solutions/insulation-for-base-walls

Probably a tad pricy for a workshop mind you.

 

[DennisCA]

I want to insulate it, because I may at some point want to use it as an office, and tbh in Scandinavia we insulate the crap out of everything and it's just nicer to be in an insulated space IMO

Will have a look at that thread

I would definitely insulate it, that slabs gonna be a massive heatsink otherwise in winter. Insulation is cheap in comparison. Also prevents the slab from absorbing too much moisture.

 

[DennisCA]

50-100mm jablite polystyrene with DPM on top then just pour your slab with a layer of mesh.

That's how I've done it as well and I will do the same with the slab I will put in my uninsulated shed too.

 

[chrisg3103]

This is the from the plans of my proposed new workshop, building warrant issued, just need to win the lottery to afford the materials now! Know 'its just a workshop' but I'd like it built to near habitable standards, in the garage at the weekend with the heater on, nice and toasty but feet were freezing

 

[Aerohead]

Henrick if you need some moderate addition of both brains and brawn on a weekend of the build more than happy to help out.

Electricity and running water are both great in my limited workshop experience, with a fridge out there could hold out a few days of it's an extra strong period indoors!

 

[DAPPH]

Henrick if you need some moderate addition of both brains and brawn on a weekend of the build more than happy to help out.

Electricity and running water are both great in my limited workshop experience, with a fridge out there could hold out a few days of it's an extra strong period indoors!

If it is a garage compatible fridge, you'll have a gentle background drying heat too providing there is a trickle of air through the building which really helps the tools & contents of the mancupboard .

 

[Henrik]

Henrick if you need some moderate addition of both brains and brawn on a weekend of the build more than happy to help out.

Electricity and running water are both great in my limited workshop experience, with a fridge out there could hold out a few days of it's an extra strong period indoors!

Currently waiting for a chap to pop around to give me a quote to dig the foundation out if he doesn’t turn up, or the quote is ridiculous I will just dig it out myself.. unfortunately the house is stupid in terms of side access - 74 to play with without starting to remove downpipes etc, and about 85 if removed

The Scandinavians have some great looking bases - insulated blocks that fit together like Lego that concrete is poured into to make an insulated base … would take a day to build it that way, but sadly not available in the UK without crazy lead time.

Another thing I’m struggling with is finding blocks that support “thin layer mortar” systems - basically glue for blocks that make the whole building waterproof. The uk blocks are not straight and even enough to allow for this, seemingly, superior construction method might have to revert to normal block walls, but waterproof aircrete blocks that have a high insulation value and take a fraction of the time to lay sounds good otherwise.

I’ll ping you if/when I need a pair of hands @Aerohead

 

[gaz1]

if i was doing it id seperate the outside walls and the inside walls

I also know that concrete shrinks as it always creates a gap when poured inside of a building

using roughly this method in this video

 

[DAPPH]

Currently waiting for a chap to pop around to give me a quote to dig the foundation out if he doesn’t turn up, or the quote is ridiculous I will just dig it out myself.. unfortunately the house is stupid in terms of side access - 74 to play with without starting to remove downpipes etc, and about 85 if removed

The Scandinavians have some great looking bases - insulated blocks that fit together like Lego that concrete is poured into to make an insulated base … would take a day to build it that way, but sadly not available in the UK without crazy lead time.

Another thing I’m struggling with is finding blocks that support “thin layer mortar” systems - basically glue for blocks that make the whole building waterproof. The uk blocks are not straight and even enough to allow for this, seemingly, superior construction method might have to revert to normal block walls, but waterproof aircrete blocks that have a high insulation value and take a fraction of the time to lay sounds good otherwise.

I’ll ping you if/when I need a pair of hands @Aerohead

Search for similar in your area ? .. these go through doorways easily they are not overly expensive either if you run it 24/7 and have plenty of lighting & fuel to see you work into the night

Doorway Mini Digger 1 Ton - Cyril Johnston Hire

The Doorway Mini Digger or Doorway Digger has capabilities approaching the 1.5 ton excavator.

www.cjhire.co.uk

 

[willie.macleod]

Currently waiting for a chap to pop around to give me a quote to dig the foundation out if he doesn’t turn up, or the quote is ridiculous I will just dig it out myself.. unfortunately the house is stupid in terms of side access - 74 to play with without starting to remove downpipes etc, and about 85 if removed

The Scandinavians have some great looking bases - insulated blocks that fit together like Lego that concrete is poured into to make an insulated base … would take a day to build it that way, but sadly not available in the UK without crazy lead time.

Another thing I’m struggling with is finding blocks that support “thin layer mortar” systems - basically glue for blocks that make the whole building waterproof. The uk blocks are not straight and even enough to allow for this, seemingly, superior construction method might have to revert to normal block walls, but waterproof aircrete blocks that have a high insulation value and take a fraction of the time to lay sounds good otherwise.

Owner operator groundworkers tend to be very good value compared to DIY. They makes less mess and get the job done in a fraction of the time of a DIYer, there is nothing worse than groundworks taking forever to dig out by hand and trenches continually needing re-bottomed after every rainfall getting deeper and deeper requiring more and more concrete.

Don't over think the base, a bit of EPS under your slab will be fine - it is cheapest insulation board type you can buy and won't deteriorate if it gets wet or react with cement. If you are wanting higher performance remember to insulate the perimeter of the concrete with some EPS as an upstand. Remember the insulation isn't going to generate any heat, it just slows down the transfer of heat so stick some UFH piping into it and feed it some low grade heat if you want the slab to be warm. I wouldn't get carried away with thin mortar systems, you need to work very accurately and that costs you in time/money compared to traditional options for relatively small gains insulation wise. Double check availability of thermal blocks locally, there were supply issues. If you want a high performing waterproof wall then again a thin layer of insulation outside a traditional block wall and a modern render system is worth looking at. I self built my house out of ICF, if I were to do it again I'd be simplifying things further by just using traditional blocks and external wall insulation.