External insulation and render

STW hive mind question incoming! Anyone in the NW/Cheshire area know of any good external render/insulation specialists? Getting big areas of damp and mould, even with nothing against external walls. Render is old and flakey. Not helped by vibrations from traffic going by the house. Came home today to find a substantial wet patch on the kids bedroom wall too.

Sorry can’t answer the first question, but would say try to work out what the issue is, is the damp just on outside walls, which walls, any roof/gutter issues, does the damp show up more when raining or high humidity and so on. Having not seen your house, it could be external render with cracks but no idea if cement based or lime, etc.

Also you can get damp showing up on old walls where previous damp has brought salts into the wall and these areas show damp. Also try and ventilate if you get mould, but harder in winter when conscious of heating bills.

If the render is the issue, see what roof detail there is for external insulation, i.e. how much roof overhang is there to cover external insulation and render, hope this makes sense.

Thanks for the input and advice. Only outside walls. Old house (1890’s) made of Cheshire bricks with render over. No idea if the composition of the render unfortunately. Cheshire brick appears to have similar properties to a sponge.

Had new fascia and gutters installed a couple of years ago by a neighbour. He’s in the guild of master craftsmen so job is top notch. I’d usually be chatting to him but he has been ill recently and I don’t want to bother him. I think any external render would need to start below the fascia board. I’m probably making zero sense here btw.

You need to find out if render is cement based or original lime based. The building fabric should be vapour open. You also need to look at ventilation and air extraction internally. Moist air internally can transfer into the walls (interstitial condensation) and can get stuck behind cement render as well as getting through cracks externally. Internally you also want lime based not gypsum based plaster and vapour open paint. At this time of year moisture can be driven internally if sun shines on a wet wall. Ventilation internally is key. Get a humidity sensor. You can sometimes check render to see if it is lime by putting some in vinegar and see if it fizzes.

Significant wet patches in the summer is surely more to do with water ingress than condensation (especially after the heavy rain we’ve had round here). You need to look carefully for water running down the outside of the walls and/or getting in from the top. It always travels down and the source of the problem may be higher than you think.

External render is usually the devil’s work unless the house was designed and built (well) with it in mind.

First things…

• Check all gutters and down-pipes. New doesn’t mean something hasn’t moved, or they are full of leaves.

• Buy a good de-humidifier! Damp doesn’t always come from the outside. I bought one of these at the back end of last year and it’s worked wonders in our house…

https://www.sealey.co.uk/product/5637198333/20l-dehumidifier

Are the affected walls on the windward side of the house?

Wind driven rain can be an issue in some areas.

6.1.6 Exposure

– https://www.youtube.com/watch?v=z53EWwDYNao –

I was gonna say exactly what muffin man has already said.

If you do decide to go for an external insulation, ours was done by R W Hough and Sons of Wrexham (we live near Delamere). Their website is currently down but they are on Facebook.

Fully recommended. The did a brilliant job.

Thanks everyone. Lots to try and read up on. Got the ladders out last night to investigate and one pipe was blocked by a bit of cement and a ball of slugs. Rest are clear and I’ll test the render and get a humidity sensor. Upstairs windows are always open or on vent. Had issues with it on and off year round since moving in

My advice, as a Building Inspector, is don’t do it! My experience of external wall insulation/render has been universally bad.

Most condensation/internal damp issues are caused by a lack of ventilation, not damp penetrating through the structure. BUT, make sure all your guttering and downpipes are functioning correctly first, and repair any defective areas of render.

Thanks core. Think we’re at the point where the render needs renewing. Bits starting to fall off and areas with lots of cracking. Will look to find what the core (no pun intended) of the issue is first.

and repair any defective areas of render.

Is this a big job? I have no idea about render (or any house maintenance to be honest!) other than the stuff on my house is looking rather worse for wear. Also in Cheshire 🙂