Outbuilding/Offie/Workshop Insulation Query

antonyc · 26 Jul 2015

Hi Everyone!

I'm building my own block building in the back garden. Everything is going well up to now - Well apart from my OSB roof getting wet today in the rain. I've covered it over with tarpaulin now.

My query is; I made the building from Quinn Lite B5 blocks (single leaf) and I want it to be insulated well because this building is going to be my safe haven and I'll be in there a lot.

My question is; Is this a good/reasonable plan?

Single leaf thermal block, battened out with 50x50mm batten, filled with 50mm EPS between the battens. Then I'll overlay 12.5mm plasterboard.

Is there anything wrong with this? Will it be overly insulated? Is that about right?

Thanks, Antony

endecotp · 27 Jul 2015

The blocks claim a thermal conductivity of 0.17 W/mK. You don't say how thick the ones you've used are; if it were the thinnest, 100mm thick, that would be 1.7 W/m^2K.

Expanded polystyrene might have a thermal conductivity of 0.038 W/mK, so 50mm would be 0.76 W/m^2K.

Ditto for plasterboard: 0.19 W/mK @ 12.5mm = 15.2 W/m^2K

The combination of the three would be 0.5 W/m^2K.

(Your battens will make it worse than that.)

The building regs require new domestic buildings to be about 3 times better than that.

Say the shed is 2.5x2.5x2.5m. Then you'd have a total wall area of 25m^2. To maintain a temperature difference of 10K to the outside, you would need to supply 0.5 x 25 x 10 = 125 W of heating PLUS more for the losses through the roof and floor.

(Please someone sanity-check my numbers!)

antonyc · 28 Jul 2015

Thanks Endecotp,

These are my calulations:

Thermal blocks: L = 0.022W/mK, Thickness = 0.11m, R = 5W/m^K.
EPS: L = 0.038W/mK, Thickness = 0.05m, R = 1.316W/m^K.
Plasteboard: L = 0.19W/mK, Thickness = 0.013, R = 0.066W/m^K.

Combined R = 6.382.

U-Value = 0.157.

But I can't get my head around the numbers. I can't convert the numbers to reality! Anyway, what I've done is got the U-Value of my house and compared them. My outbuilding is way more energy efficient.

Although, one of us is doing the calcs incorrectly... I'll try to research this more to find out who!

endecotp · 28 Jul 2015

antonyc said:
Thermal blocks: L = 0.022W/mK

Where does that number come from?

antonyc · 28 Jul 2015

You're right! I have no idea where that number came from. It's a value I written down ages ago when I bought the blocks. You have the correct value and the correct U-Value.

endecotp · 28 Jul 2015

Consider using something like Kingspan K17. The insulation has half the conductivity of polystyrene, and you don't have thermal bridging due to battens if you glue it onto the block work.

antonyc · 28 Jul 2015

Ohhhhh errrr.... It's £40 a sheet!

endecotp · 28 Jul 2015

Compared to how much for polystyrene + plasterboard + battens ?

antonyc · 29 Jul 2015

EPS £7 a sheet from local builders merchant.
Plasterboard £5.40 a sheet from B&Q.
2x2 PSE £3.40 per 3.6m length at local BM.

endecotp · 29 Jul 2015

Well you can do the sums.... and also consider how long each construction method will take.

endecotp · 29 Jul 2015

(You may find other polyisocyanate boards that are cheaper than the Kingspan.)

antonyc · 29 Jul 2015

Thanks! I'll check out more prices. Thank you!

noseall · 29 Jul 2015

If you are flapping about prices v's a space you can actually use long term, then you are approaching this with the wrong mind-set.

However, if you want a mouldy, damp smelling, gloomy hole where any paper-work, electrical equipment, cloth seats, carpets etc, become unusable and ruined after one Winter, then crack on.

Spend wisely - spend once. The closer you get to achieving the latest B'regs standard, the more efficient and better the structure will be. £1'100 p/m is the going (cost) standard. If you were thinking of a budget of say £100 p/m then forget using this space as anything other than a shed to store empty paint cans.

noseall · 29 Jul 2015

Incidentally, I think your insulation spec' is pants. Slightly better than a garden shed.

antonyc · 29 Jul 2015

noseall said:
Incidentally, I think your insulation spec' is pants. Slightly better than a garden shed.

There's always one isn't there?

I actually have another building which is single leaf brick without any insulation which has paperwork, electrical equipment, etc in it and it's all fine!

But I get your point.

diynot

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Outbuilding/Offie/Workshop Insulation Query

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