DIY EWI (Exterior wall insulation) hits and tips

[i_am_fubar]

Planning on putting a 20mm EWI system on my block built workshop. After some confidence boosting tips.

Are there any gotchas or preferences peeps have to offer?

Silicone render or dry mix render with paint? Which is easier?

Any decent tutorials or step by step advise for dealing with doors & windows? Most guides I've found are "Assuming a flat, smooth wall with no corners or windows" and not much use for actual application.

Ta,
Fubar

 

[endecotp]

20mm isn't very much.

 

[Jurassicspark]

I installed 100mm EWI on solid walls. 20MM isn't much to be honest. I used silicone render to finish it off.

You'll need a lot of expanding foam to fill in gaps. All lights, outside pipes will need extending if you go for 100mm insulation. If it involves a gas pipe or flue then you'll need to consult a gas engineer.

I changed the old cast iron waste pipes to plastic during the process. You will also need to create a roof overhang as the insulation will overlap the existing one. All window sills were replaced.

As you mention it's a workshop the job should be much easier and would not require scaffolding.

Have you checked if the wall is actually solid?

 

[i_am_fubar]

Addressing multiple points from the replies (Thanks folks)

"20mm isn't much" - agreed, but I've got 50mm gap on one side to fit the full system in and an alleyway on the other side that I can't afford to loose much width from. R value of the blocks is ~0.09, R value of 20mm EPS is ~0.48, so while not much, it's 5 times better than none. It also gives me a little more sound isolation and waterproofs the outside

"Is the wall solid" - I had a big argument with architect (me) and the builder (also me) and grudgingly came to the agreement that it's single skin 100mm concrete blocks.

"Roof overhang" - it's a flat roof, yet to be added, so I'll just extend the fascia over the render. that's getting a solid block of 100mm PUR in a warm deck.

"Protrusions" - the only protrusion will be 10mm SWA coming in which I'll fit after the render is complete so I can drill through and seal during wiring.

I'm looking for thermal stability, hence many tons of concrete with the insulation outside. I could possibly go up to 30mm, but it'll be a squeeze to get the rendering finished between wall and fence posts.

I'm still trying to work out how the window & door trims work. I get the adhesive sticks it to the uPVC, but then there is another bit of self adhesive that looks like it folds over or gets torn off.

 

[cdbe]

Unless you're planning on heating it like a house you might be better insulating internally - that blockwork will soak up a lot of heat before it gets stopped by the insulation. If you insulate internally, combined with something like a fan heater it will warm up quickly and be (reasonably) economical for irregular use.

I did my prefab garage with 50mm internal and over boarded with 18mm ply so it's great for fixing shelves etc to.

 

[i_am_fubar]

It's a fair point cdbe, but I'm after thermal stability more than warmth, and I want to use the mass as a thermal battery. fluctuations play havoc with machine tools and condensation. I may put a low power heater in to keep it up a few degrees, but nothing close to domestic heating levels.

Other points are that 1) I'll be doing welding, so non flamable wall coverings (i.e. blocks) are preferable. But it'll also eat into my available space and I'm already struggling to fit everything in.

 

[mrrusty]

and I want to use the mass as a thermal battery. fluctuations play havoc with machine tools and condensation

Thermal mass can also be detrimental. If you get a cold winter spell your garage could easily drop to a few degrees unless permanently heated. Insulation won't stop it cooling with the weather, it just slows down the temperature change. If the weather suddenly warms and becomes wet (and we've all seen it - a day of 12-15 degrees, raining, after a cold snap) your nice insulated garage is now, because of the suddenly changed weather, at 12-15 degrees with high humidity outside and because of the insulation perhaps still 3-4 degrees inside.

Open the door, and instant condensation on all the still-cold surfaces. In this situation insulation has worked against you. You would be better off without any insulation allowing the garage to quickly warm to ambient at the same time as outside eliminating the temperature difference and condensation risk.

Bottom line - you either heat it like a house and keep it above 12 degrees or so all the time (or as much as possible), or there is no point in insulation at all.

 

[i_am_fubar]

Fair comment Rusty, though if you only ever heat your house to 12, you're hardier than I am. My goal was to keep it ~12 ish at all times with a small space heater. And regardless of insulation, it's the the thermal mass of the tools that has caused my plague of rust. But a couple of harsh temperature swings a year will still be better than months of daily warm/cold cycling surely?

 

[mrrusty]

though if you only ever heat your house to 12, you're hardier than I am

The reason you try and keep a house above 12 degrees is because that is the temperature that ambient room air in an average house - say 20 degrees and 60% relative humidity will start to condense out as liquid water. It's why the cold corners on external walls are the prime spot for black mould as quite often, at night, they get colder than the dew point.

Thermal mass only affects condensation to the extent it influences the thermal "inertia" - how fast things heat up and cool down. Things with a high thermal heat capacity like water and metals will cool and heat up more slowly than the air itself. If you can keep everything at 12 degrees you are fairly unlikely to see condensation problems, but always possible. If your garage is all at 12 degrees, and the air outside is 15 degrees and raining (i.e. 100% humidity), you will still get a small amount of condensation if that saturated air at 15 degrees hits a surface that is at 12 degrees (i.e. below the dew point).