What to do with a single skin utility room?

[bikenrrd]

We bought a fixer-upper of a house 3.5 years ago.  We fixed everything up (a big job - electrics, windows, removing a wall, new boiler, decoration throughout etc.) within about 18 months, except for the utility room.  This is a single skin room, tacked onto the back of the kitchen, and has a problem with damp.  It also has a toilet in there, walled off from the rest of the utility.

When we got new windows we also got double glazed units in the utility room, which are too small to have an opening.  One has a trickle vent.  The utility is single brick constructed with a poured concrete flat roof.  There doesn't seem to be any water ingress from the roof.

What would people suggest to remove the damp?  The whole room requires replastering as it has a kind of concrete render on the inside which is falling off in chunks.  I can think off:

1. Fit an air brick.  The cheap option.
2. Fit a dehumidifier with permanent drain into the toilet soil pipe.
3. Insulate the roof by boarding and stuffing with rock-wool / other insulation.
4. The expensive option - insulate the outside.  There's not enough room to insulate inside.
5. Repoint the outside, just in case.

Any other suggestions?

[mrcharly-YHT]

Sounds like the brick walls are damp.

Does it have a DPC (injected, plastic sheet or bitumastic mortar)?

Water ingress from flat roof is common. The felt/waterproof layer can be intact but around the edges it is leaking onto the top of the bricks. Is the render falling off evenly or from one section more than another?

You need to sort out the damp in the walls first.

You really should have an air brick anyway.

I'd be inclined to hack the cement off, clean the brick and paint with emulsion initially. Even if the brick is still damp, the emulsion will let the damp through. In a utility room does it matter so much?

[air dancer]

I'd go with fitting an air-brick firstly. Unblocking air-grates in cellars can work wonders on controlling the dampness. Kind of similar.

Ensure the outside fabric of the extension is watertight.

Got central heating? Perhaps adding a small radiator in there to lift the temperature enough to push the moisture away.

[bikenrrd]

Cheers.  It has a damp course sheet - you can see it poking through the bricks on the outside.

It already has a small radiator in there - as well as the (condensing) boiler and washing machine.

The render is falling off on one side only.  This is also the side which has the most mould, which is behind a bin, but raised above the ground.

It's a bit of a shonky lean-to, really.  If we had had more foresight we would have ripped it down and replaced it with a room with a cavity wall and pitched roof!  Having a 2 week old child we don't want to lose our only source of hot water (combi boiler) so can't really do the work now!

[Ian H]

Dry-lining might be the simplest option.

[mrcharly-YHT]

The render is falling off on one side only.  This is also the side which has the most mould, which is behind a bin, but raised above the ground.

Is this on the north (or shaded) side?

I suspect either rising or falling damp on that wall.
An airbrick will help.

[air dancer]

I'd do a DIY fix of that rendering too. Waterproofing additives are available for the mortar mix.

[Wombat]

As its single skin, you will never get rid of the damp until you do something serious to the outside of it to keep the moisture at bay.  Airbricks, heating, dehumidifiers, are all only ways to cover up the problem, not cure it.  You are right, hindsight is a wonderful thing, yes you should have sorted it when you did other work....

As a low-ish cost start I'd go for making sure the external pointing is all up to scratch, and then using something like Thompsons water seal on the outside.  A proper waterproof render, or far better, insulation and render would be the best bet short of total rebuilding.

[Quisling]

+1 to Wombat's post. Could consider humidistat controlled extract fan as alternative to air brick and less draughty. Approx £80-£100 in Screwfix for a high efficiency fairly quiet model. But fix the reason for the damp first

[Canardly]

Dry lining and turn that conc roof into a warm roof. (ask your roofer) You will lose some floor space but be much more comfortable and your heating cost will shrink a little. You need to ascertain if is penetrating/rising damp or is simple condensation on cold surfaces. People tend to refer to 'damp' universally  but these are very different things. What is your budget? Have a look at Matilda's blanket. Not cheap but very neat solution. Consider also a warm floor covering e.g. cork.

http://www.greenspec.co.uk/building-design/concrete-flat-roof-insulation/

[Bugloss]

Post a few photos of it and the damp problem.

[Asterix, the former Gaul.]

Render?  Has it been rendered down past the DPC?  If so then that is a bridge over which damp certainly can rise.  A simple answer is to hack off the render below the DPC and a little above.  It is then possible to retro fit a drip strip so water running down drips off before reaching the DPC.  You can get steel drip strips that you tack to the wall then render over.

Porous brick walls can also be treated with silicon that you simply brush on.  This repels water whilst allowing the wall to breathe.

[Asterix, the former Gaul.]

Dry-lining might be the simplest option.

with ventilation behind the dry lining, I'd suggest.

[Bugloss]

Sort the damp problem out first before you do anything else.