Solid Wall Construction and Insulating it

[jase the space]

I am looking into insulating my solid walled extension (of a 1936 cavity walled house – not sure of the date of the extension) in the next few months to make the bedroom more habitable for a new arrival!

At the moment the room is very cold and I suspect it has a damp problem – there is polystyrene lining paper on the walls which is coming away slightly in places. Not sure if this is due to general condensation in the room or whether there is penetrating damp through the external wall. At the moment the room is used as a junk room and I haven’t had a chance to investigate thoroughly yet.

Wall Construction:

I believe the solid wall is twin skin so I guess around 9" thick (?). I have several vented bricks in the wall that can be seen externally but have no opening inside – I have tried to find out what these are for by searching the internet for various construction techniques but can’t find anything that might match. I am wondering whether there is a small cavity behind the plaster that needs venting to prevent damp? The funny thing is the vents aren’t very regular on the walls – clay brick vents for each floor on wall1; none on wall 2 (although it has a 1st floor sash window and maybe the gap around the window was used as a vent – subsequently blocked up with sealant!); 1 metal vent cover on ground level only on wall 3 (and a ground floor sash window with sealed up gaps, plus a kitchen door); wall 4 is the original external cavity wall that is now an internal wall. I would appreciate any theories anyone might have on this!

When I installed a vent for a tumble dryer in the kitchen downstairs I noticed there was a corrugated black fibrous liner fixed to the solid brick inner face with plaster applied directly to this. My assumption was that this was a damp proof liner. I’m fairly sure there wasn’t a cavity behind it (referring to my comment above) other than that caused by the corrugations themselves.


Insulating:

I have looked at the various techniques and have come across the woodfibre boards method (internal) - e.g. Pavatex/Pavatherm/Diffutherm. These are supposedly good for the environment (recycled materials, clean energy used in production and they lock up carbon), breathable (no vapour barrier needed and no special ventilation required), resilient to damp (work even when damp and can act as a moisture buffer to keep internal air quality good), good acoustic indulation properties, improve the thermal mass of the structurem, and are non-toxic. They are more expensive than conventional materials though and require special plaster to maintain the breathability.

Has anyone here had any experience with these?

Should I just go the conventional route? Laminated thermal plaster board or separate insulation + plaster board? What thickness?

Can anyone give any advice on how I should proceed with respect to the construction of my extension walls? i.e. should I remove all existing plaster and liner and start from inner face of brick? Would I still need the vents or could I block these up?

If I have a penetrating damp problem would woodfibre be OK to use (breathable) or would I need to fix the damp problem first? Or maybe maintain a vented cavity?

Is DIY installation possible? I am fairly competent at general DIY but I have never done dry-lining before (I would get someone in to do the plastering anyway)? Would a general builder be able


Any advice would be appreciated.

 

[Darkrob_DIY]

I would think that you have a condensation problem - best idea would be to unblock all vents and make sure they have a good circulation into the room.
This will help to get rid of the moisture laden air in the room and will stop the condensation - can get hit/miss ventilators.

The fibrous layer that you mention sounds like a DPC possibly bitumen?? The plaster should not bridge this layer as this can lead to rising dampness.

I have no experience with the insulating systems that you mention, however once the condensation issue is resolved the traditional method of insulating with vapour barrier/air gap would work appropriately.

Hope this helps

Rob Critchley

 

[jase the space]

Rob

Thanks for the reply.

As far as I am aware and can see the vents haven't been blocked up, they just don't seem to go anywhere! I can see them on the outside but there are no vents inside - this is why I was wondering if this was just a weird form of solid wall construction (along with the liner).

I had wondered if the liner was bitmen and used as a damp proofer but can't find any mention of this form of construction anywhere. I always thought a DPC was used along a course of bricks to stop rising damp - this is a full wall liner presumably used to stop penetrating damp.

If this is a damp proofer then do I have to keep it there and put all insulation on top of it? Do I need a cavity to vent any damplnes away?

Anyone else have any experience of woodfibre boards?

 

[Darkrob_DIY]

Sorry i misunderstood bout the fibrous liner, i thought you meant it was fixed between courses of bricks not actually fixed to the brick face.
Cant say ive ever heard of something like this im afraid

 

[JohnD]

It used to be the practice to put air bricks at the top and bottom of the outside leaf only to ventilate the cavity and kep it dry.

Since this led to increased loss of heat the idea has been dropped now. Many cavities are filled with insulation and if the wall is in fair condition none the worse for it.

However:

It is also very common for airbricks that penetrated the wall and ventilated the rooms to be blocked up. This leads to poor ventilation and often condensation and damp.

Give one of your lower airbricks a poke and see how far the cavity seems to go. If tyhe wall is solid not cavity then the airbricks can only have been intended to ventilate the rooms (or food storage cupboards, in kitchens)

If you have damp rooms and blocked airbricks, opening them up and fitting a hit and miss ventilator to prevent draughts in windy conditions will do a lot of good.

The bituminous liner fixed to the wall sounds like an anti-damp system sometimes found on basement walls, odd to have it on an ordinary room.

 

[jase the space]

Thanks all.

So if the liner is indeed there for damp proofing and the vents have been blocked up from a previous renovation (?) should I:

1) Maintain the liner? If someone were to build a twin skim solid wall these days would they have this liner? If not how would they deal with penetrating damp - would they have a vented cavity behind some dry-lining for instance?

2) Get rid of the vents altogether (i.e. replace with normal bricks) or open them back up into the room? Again if someone were to build a solid wall today would they have vents like this? Is there any other way of venting a room without vented bricks? Do I need this ventilation at all?