Garden Room Workshop Extra | Insulating A Concrete Slab

Thermal mass is an interesting topic so in this video we take a look at the placement of insulation in a concrete slab, with a slant towards doing so for a garden room in the UK.

Some extra notes that would have muddied the video had I included them:

1) Adding any kind of underlay or flooring (laminate for example) over a concrete floor will reduce the thermal mass properties of the concrete underneath. The biggest effect will come from an uncovered slab (for better or worse depending on your climate and use of the building).

2) The diagrams are not to scale but are reasonably accurate. The first option should have insulation up the sides to insulate it from the ground to the sides. Also whether you have a DPM/vapour barrier above the concrete will depend on whether the concrete has fully finished curing or whether you know if there is a DPM under the concrete (an old shed concrete slab for instance). If in doubt add another on top, it won't hurt.

3) All of this is just my layman's opinion. I like science, geography and construction and put them together with a bit of research. You can't go too far wrong with any of the options though 🙂

0:00 Intro
0:14 insulation choices
0:46 The 3 options for placement of insulation
1:13 What is thermal mass?
2:12 What is the roof overhang for?
2:31 Choosing the best option
3:30 Other pros & cons
4:29 Outro

[azmirfakkri]

Great video for someone who has no idea on how to insulate a floor! Thank you!

[matthaslam]

Ok, that was the most useful flooring insulation video I've seen. Thanks for that!

[MDMD-uzbu]

Finally a video that explains options to avoid confusion

[mikeforwarduk]

Really, really helpful and wonderfully brief. Good job!

[Reef_Club_]

Genuinely brilliant videos - so helpful

[aesopshair]

Thanks Ali, great video!
The use of 'thermal mass' is a default option that has arisen due to the way houses have been built over the past few centuries; it is now possible to control the internal environment more effectively and efficiently which reduces the requirement to have thermal mass for temperature stability purposes.
Interestingly, water is the material with the highest specific heat capacity (over 4x that of concrete), so having a well insulated water tank is an effective way of storing heat energy for use at a time when required, rather than constantly heating the floor slab of a thermally leaky building.

[qshed]

over the summer we built a sun room(3×2.5m) on the back of the house. As one of the kids will use this as a bedroom when back from university we opted for the 100mm concrete over 100mm of insulation. Electric underfloor heating (1200w) then a 65mm screed. It takes a couple of hours to warm up but stays warm for 8 hours. so great for overnight. next job is solar panels to offset the heating costs.

[mattpage]

Been looking forward to this since you mentioned it a few videos back, thanks for uploading

[mikedeman]

Nicely done. I think it would be good to see a video where the insulation of floors, walls and roof is discussed in an integrated way, in order to eliminate thermal bridging. Maybe an idea for a future video. You have a knack for clear presentation.

[greenambles]

Thanks! That'll be option 3 then. My cement pad going down in the next couple of weeks 🙂

[georgecorden]

Absolutely not geeky! This is a life saver really. I’m building a shed which is going to be more of a utility room with washer and dryer and various other appliances along with tools. I’m going for option 1 as it’s a shed and I think it will be ample

[rikgeartv]

Thanks for the video.
I'm drawing up plans for a 7.5m x 3m workshop in my garden (central England), my first thought was option 1 and found this while searching for other options. The considderation of the slab being a heat sponge during the initial heating I hadn't considdered.

However, There's some heavy equipment going in that will need bolting down (like a fly press) so options 2 and 3 are out.
Also, as the building is going to be within 2m of the property boundry (right up against the fence on 3 sides), I'm limited to 2.5m hight, so the lower the floor the better.

I've been using some old gym floor matting (about 15mm thick dense rubber) in my rented space as fatigue matting and this could work to dampen the heat transfer issues as well as dampen sound.
And if converted to a garden room at a later date, would make a good underlay for laminate.

Heating wise, my first choice is a cheap deisel heater and this will probably be installed anyway as it's a cheap option for a usable space asap. What I'm thinking now though is when fixing the roofing sheets down, install some brackets at the same time for future installation of solar panels to power ceiling mounted radiant heater panels or convector heater to take the edge off, and use the deisel heater as a booster for extreme cold weather...

[tufty]

Love this video! I have gone for option one but I will probably add some thermal underlay just to top it off. I need to get some pictures over at some point!

[sheppodiddly]

Very good. Clear and informative. Will be using your advice, thanks!

[MikeFromDublin]

Hi Ali, I'm working on a variation on options 2 and 3 for a workshop that I want to heat occasionally. I'm thinking of using foamed concrete instead of normal concrete, which will give me much greater insulation value. My main challenge is the design of the perimeter which has to hold the weight of the building - probably a shallow foundation and 100mm half-blocks. Great series, really useful, thank you.

[BSKiteHaps]

Loved learning more about insulting a floor. Thanks

[JamesMedcraft]

Thanks @AliDymock

This is a really useful video, thanks for taking the time to make it.
Could you share the link to 'Nick's Build' which was the chipboard/insulation on a concrete slab? It's at 04:41 in your video.

[paulghampson]

Really helpful to understand the choices!! Thanks

[leethacker]

Learning as I go along, I've used option 3 during my build but that's more because I just thought that was 'the way' and didn't realise there were other options. Working out well though!

[matthewvarley]

Hey Ali, was just trying to check out the website, I'm stuggling to connect, just wanted to have a look at Nicks Build, cheers for the most in depth series in diy