Help please, comments please. Sorry it is long.

My son has a small 1890s two up two down semi and has damp spots on paint in upstairs and downstairs back room to side of unused chimney on gable end wall - it is only single skin brick away from chimney areas.
We think condensation is due to cold spots and they tie up with dabs at back of plasterboard. He painted about 6 months ago and did not see damp spots on old paint but they started coming as weather has got colder this year. He has been in just over a year.
Questions
1. Should he apply some other paint that deals with condensation better - if so what. Current is Dulux standard emulsion
2. There is air flow behind plasterboard - with single skin brick then to outside. Is it OK to stop the air flow and foam around the plasterboard ? Worried as it is likely to be helping to dry things out ?
We will trial stopping it with gaffer tape anyway and thermal camera the wall to see if it take cold spots away or could the inner wall then get damp ?
3. Is vent on unused chimney to outside a cause/part of problem - should it be to the room/inside
It gas capped ventilated chimney pot. No damp on actual chimney internally
4. Can waterproof breathable treatment be used on the rest of wall - lower half has been done based on tests yesterday
If so is this OK with lime mortar he is looking to use longer term to repoint this wall currently cement pointing

Humidity 65 ish at about 19 C when heating on. We are going to log this for a bit,
Extractor fans on in upstairs and downstairs bathrooms on small rear extension are being used as well as a dehumidifier (refrigerant based) - generally think internal humidity under control but logger starting to be used to confirm.

Detail
He is generally looking to upgrade thermally and preserve the place. There is no space outside to EWI as too close to neighbours land/ fence. Also the brick is very nice and part of the places charm. Wall faces South East.
He is looking to insulate the unused chimney as per recent GBF thread.
Damp patches to side of chimney on one side of unused chimney at rear upstairs and downs stairs.
At centre of house is stairs with landing attached to this gable end wall. Cold understairs cupboard is to the side of the patch the unused chimney the other. The air brick might be part of this coldness – see later
2 patches of plasterboard in damp areas removed yesterday in upstairs and downstairs rooms. Behind is bare brick - which is dry and plasterboard is also snuff dry. Just surface condensation causing damp it seems.
There is a draught behind plasterboard. Down stairs found small air brick 3x9 on outside and also above damp injection coarse at just above floor level a series of hole drilled that go though to the plasterboard. This nearly went when gaffer tape put on 3x9 air brick. Air bricks does not vent into under-stairs cupboard probably into plasterboard
Upstairs - gap to loft if likely to be the cause of the air flow behind plasterboard.
In loft he has found gap open to loft about 10 mm and same sort of draught on removed - gaffa tape going to be applied as a trial to reduce air flow - to see if it warms wall and takes away the condensation spots.

Single skin brick found on outside wall but a far it of wall is covered by chimney as well.
It has plasterboard dot and dabbed and was refurbed some 6 years ago
- chimneys in both downstairs and rooms - these come together in loft
Front room has log burner - just swept by a good guy who gave installation all clear on liner etc.
Not used everyday but reasonably often
On back room chimney air brick 6x9 to outside wall - Not sure why not to the room which I think is the norm
A brick is out in loft on unused chimney.

Lime mortar due to age but has been repointed in cement at various times - mostly in good condition
Based on fact it did not fizz when vinegar applied we are saying it is cement - not expert knowledge.
Lower story/ 8 ft of brick has been coated as it beads up and repels water - upper part not coated we went up with a ladder yesterday

Damp proof coarse has been put in in past - no signs of wet coming up. (if it ever does)
No sign of wet coming through the wall as penetrating damp through the single skin
Roof in good order - chimney stack looking ready for some love but flashings all seem OK and nothing came up on survey

Thermal camera on outside of wall showed no massive heat leaks - just all warmer than you would think.
14 on areas near working chimney that had been lit night before. 12 to 13 on the rest of the wall. Say 5 C outside temperature.
On inside dot and dabs downstairs were about 14 C

I think that we are looking at condensation

Tony's test to validate theory would to stick a small piece of broken glass (above puppy height) to the wall over a damp spot fully adhered with say acrylic sealant, then see if the surface of the glass get dew on it and report back

The blobs of the deadly blob and dob will be colder than the intervening plasterboard as they are cold and in contact with the brick wall so more prone to collect condensation. the corner of the room will be least well ventilated place and could be colder as the cupboard will likely be cold too.

Thanks Tony and Will. I am not experienced in old buildings and lime mortar or single skin. We are treading carefully and moving slowly. If it aint broke do no fix it springs to mind here - it is complex.
I now think it has solid plaster at lower level probably damp proof stuff when damp proof layer was done and only plasterboard at higher level - which seems it will stop walls breathing more.

Tony - My son Andrew is putting glass on as we speak- to see if dew forms on the glass at the cold spot.
Thermal camera attachment on phone is showing clear cold spots so expecting it to confirm condensation.
Andrew scraped paint off damp areas - Also trying to dry the patches to get rid of staining on paint.

Might just be a bit of a weird paint reaction on damper spot ?
Old paint prior to this just seemed standard emulsion based on what he found in shed.
Previous owner is friendly and we are trying to find out a bit of history. They did not do the plasterboard refurb.

Will - is it rain penetrating damp ? the wall just seemed dry. The mortar very dry - some powdery etc. No obvious signs of ingress of water had a pretty good poke around everything from ladders. Paper backing on plasterboard cut out is mint. It has been very wet recently so

Today he is doing trial on temporarily blocking draughts behind plasterboard to see if this warms up the spots.
Low level holes in bricks on outside above damp proof coarse (is this to dry out bricks but they go right through)
Gaps between wall and plasterboard in the loft with paper for now.

I can prove damp in the wall easily , I drill a hole 50mm into the brick, collect the dust, weigh it, dry it in an oven, re weigh it , calculate % moisture

I can do it by post if you collect sample and put it in a self sealed snappy bag and send it - I think the wall is dry though

I think that the wall is a solid 9" brick wall (single brick generally means 4" wall to me)

Thank you all for input.
The side gable we think is single brick. Front and back is 9 inch ... This has doors and windows in. These seem ok.
The side gable is buttresses by the chimneys and by the central stairs we think ... say 2/3 is single skin 4 inch.
Two neighbours with same houses advised single skin. We will check more to confirm.
Tony. Good idea about before and after oven weight.

If chimney vented from warm room it would increase ventilation and warm the chimney. There was a recent thread on filling unused chimney with insulation. Is this possible here ?

Posted By: tonyThere needs to be a change in the law to allow EWI in this circumstance

There seem to be 2 issues with EWI in this case, 1 problem with space/distance to neighbours and 2 the aesthetics of a brick wall going to a rendered look alike wall.
I if distance to the neighbours is an issue providing the added thickness doesn't overhang the boundary (is the wall within 100mm of the boundary?) then I believe you are entitled to access your neighbours property for the purpose of maintenance so installing EWI should not be an issue. and 2 The asthectics is one of personal choice and/or PP. each circumstance is different. For me, looking at the pictures I would EWI the end wall but leave the front especially as it is a semi.

Posted By: Peter_in_HungaryThere seem to be 2 issues with EWI in this case, 1 problem with space/distance to neighbours and 2 the aesthetics of a brick wall going to a rendered look alike wall.
I if distance to the neighbours is an issue providing the added thickness doesn't overhang the boundary (is the wall within 100mm of the boundary?) then I believe you are entitled to access your neighbours property for the purpose of maintenance so installing EWI should not be an issue. and 2 The asthectics is one of personal choice and/or PP. each circumstance is different. For me, looking at the pictures I would EWI the end wall but leave the front especially as it is a semi.

I agree with PiH. There's also the possibility of buying a narrow strip of land off the neighbour if necessary. A lot depends on the neighbour's attitude.

The aesthetics can probably be overcome by using a brick slip finish on the EWI.

<blockquote><cite>Posted By: djh</cite><blockquote><cite>Posted By: LF</cite>4. Can waterproof breathable treatment be used on the rest of wall - lower half has been done based on tests yesterday
If so is this OK with lime mortar he is looking to use longer term to repoint this wall currently cement pointing
</blockquote>
Sorry, missed this earlier. Yes it'll be fine.</blockquote>

Hi - we are reading scary things about silicone/flammable water sealers on lime mortar versus more vapour permeable porous waterproofing water based products.

It seems water based ones go in about 20 mm and standard cheaper ones are a couple of mm and more surface based. Do we cut in to find out or is there another way of working out what is on there. Andrew talking to previous owner to try and find out. Checking if Tony glass is wet and calculating what dew point has been each day from data logger thing I have lent him.

We are not going to do anything quickly here. Currently capturing data to get baseline RH/Dewpoint / outside inside temperatures, weather and wind and is surface damp growing or retreating etc. Will then seal the air gaps behind the plasterboard and from loft to plasterboard. See how much warmer it gets.

We are thinking get the window to be the coldest spot in the room so that will drop out water before going on walls.

Situation is not terrible, no mold or smells or signs of imminent damage - just blotchy paint !

Commercial situation - Andrew is first time buyer and young so funds are an issue too. Survey did not pick up single brick thick wall or people we asked to have a look at. He wants to keep place long term and rent it out when they outgrow it. Condensing boiler and wood burner and bills not too bad. Solid concrete in floors !

EWI - might be able to get 100 mm of neighbour - his side pathway is pretty tight
Might be an option to do on the whole wall but then solid 9 inch walls may need attention.

As I say we are gathering data and understanding for now. Thanks for all input.

Posted By: LFHi - we are reading scary things about silicone/flammable water sealers on lime mortar versus more vapour permeable porous waterproofing water based products.

I'd be interested to read those if you have any links?

I would use silane siloxane type.

Looking at the side wall picture it appears that there is a narrow path down the side of the end wall that looking at the fencing belongs to the semi in question. Whilst this is narrow would the loss of 8 or 10 cm for EWI be a tragedy? I would suggest fixing OSB sheet sideways on to the EWI after the adhesive/mesh coat and before the thin film render and then thin film render over the lot. This will give mechanical protection to the lower 1.25m of the EWI. (I have found that the thin film render sticks very well to OSB) All this would need from the neighbour is permission for the scaffolding or tower to be part in his drive for the duration of the works.

I can quite understand the reluctance to EWI the front wall.

Posted By: lineweightLook at that lovely brickwork with the corner details and everything! Please don't EWI the side - it'll look awful.

Yes, saving the lovely brickwork is so much more important than saving the planet.

Posted By: WillInAberdeenOr do careful IWI, and save them both, whilst keeping warm?

Sustainability is about conserving cultural heritage *as well as* natural heritage *as well as* meeting the needs of the present *and the* future occupants, not *instead of*.

BTW I think LF is quite right to take careful steps, not rush into making major 'modernising' changes to a building that has already lasted several lifetimes. Previous generations who put cement pointing or pebbledash onto walls like that, are not thanked for it now.

Yes.

Posted By: LFIf we make this wall warm, then front and back may become coldest and then move the condensation problem or to some other cold bridges.

Yes, if you insulate the end wall the condensation will then move to the next coldest place -however it will be less than on the end wall because it will be inherently a bit warmer than the end wall was.

With a single brick wall lined with ventilated plasterboard the wall must be horribly cold in the winter and cost a fortune to heat the place - plus probably be uncomfortable to sit near.

If the eventual aim is as a rental property then I can't see an acceptable EPC rating (to comply with rental regs) without doing something to the end wall so something (insulation) will need to be done anyway. To get sufficient insulation as IWI will take up room space that you probably don't want to loose - especially if some IWI is needed on the front (and back?) walls to meet the regs. so long term IMO the best would be EWI, which can be done DIY or part DIY if you don't feel up to the rendering bit.

Posted By: djh

Posted By: Peter_in_Hungarythe rendering bit

Or do away with the rendering bit and the aesthetic challenge by using brick slips.

That kind of misses the point... you can't easily recreate historical brickwork with slips and even if you could, the additional thickness would mess up the proportions and you'd end up with odd details like a fat chimney, how to deal with that corner with contrasting bricks and so on.

The choice is between compromising the interior space a little (and doing a more tricky insulation method) and compromising the appearance of the outside of the building, which forms part of everyone's shared public realm.

Of course, how important the external appearance of buildings is, is subjective so there will always be a difference in opinion what the greater compromise is.

If the front wall of the house is potentially being considered for IWI...then there is a logic in continuing this along the side wall, to avoid a switch in systems and discontinuity of the insulation layer.

It's different for every property of course... but to me, the best strategy often appears to be, modest IWI to walls which are externally attractive and seen from the street, and perhaps generous EWI to the rear, which is usually more utilitarian in appearance, and more likely to have been already modified with extensions and so on. And then, as much insulation in the roof as you can manage.

Thanks all.

Rear extended part and rear elevation are painted white and needs attention so that is possible to EWI.
Cost seems high looking through threads on here of the order £100/m2 installed.

Is there a low cost supplier of materials only. We would get someone to render cost effectively and well.

Side elevation - not my call. We are checking front lounge tonight as we think there is some IWI insulation used and no damp spots in that room. I think log burner will be drying that out as well though.

Government help on insulation at the moment might be of use - need to read up on details. Suspect funds will be very tight to do anything at the moment/ important factor.

PinH -thanks for advice on rental and houses EPC rating being important, had forgotten that.
Side wall looks like an easy flat wall to cover, if that works out to be way to go.
Chimney is internal - does EWI not just go over it or does it need some special detail ?