Dot and dab cold spot / damp?

[Doggit]

It may not be damp on the party wall; it's possible that it's excess moisture in the room settling out on the cold spots of the dab.

 

[Guyray]

Do you have breathable membrane on the roof?
Keep the trickles open on the Velux. It's probably more a case of insulation and a robust method of achieving a VCL.

Sorry, I missed this. I'm not sure if I have a breathable roof membrane, but the roof is 8/9 years old, the membrane is green. How else can I tell? The veluxs don't have trickle vents!

 

[Guyray]

It may not be damp on the party wall; it's possible that it's excess moisture in the room settling out on the cold spots of the dab.

Thanks doggit. How do I tell?

 

[noseall]

The veluxs don't have trickle vents!

The first click on the bar handle is a trickle vent.

 

[Guyray]

The first click on the bar handle is a trickle vent.

Ah! Great.

 

[Doggit]

It's not so much how you tell, more of just determining the best way to go. If you haven't got the trickle vent open, then how are you ventilating the place. If it is excess moisture in the room, and you don't deal with it, then it'll just settle out somewhere else when you insulate the cold wall.

 

[Guyray]

It's not so much how you tell, more of just determining the best way to go. If you haven't got the trickle vent open, then how are you ventilating the place. If it is excess moisture in the room, and you don't deal with it, then it'll just settle out somewhere else when you insulate the cold wall.

I see. Noseall may have saved the day with the news on the velux trickle vents. The room does get warm in summer, it's a 4 bed house. Do I have consensus that pointing, dpm painting, vcl layering, battening and boarding is the way forward? Maybe I should salt neutralise chimneys too?

Thanks all!

 

[vinn]

OP,
I dont know where the damp is coming from - thats what I'm trying to find out.

Is the gas appliance connected to a SS flue liner?
Every room with a chimney breast will have a separate flue and fireplace. Count the stack terminals if you still have them on the active flue side - six terminals means six flues etc.

Did you and the neighbour's both have new roofs a few years ago - why?
Was the parapet done at the same time or later?

The consensus was that the Titanic was unsinkable.

 

[Guyray]

Good point. Not sure about a flu liner. Thanks for info on stacks. Only our roof was new as the loft was converted. His wasn't. His parapet was cracked all over, so he had it re rendered last march, our was repointed, along with the flaunchings tidied, stacks pointed and flashings checked. I know very little about flus etc, and their influence on damp. I've read a bit about hydroscopic contamination. Thanks for your time too Vinn. Greatly appreciated.

 

[chappers]

Looks like cold bridging to me, you can even see some of it starting to form along the long vertical joints where the boards meet. One way to find out for sure is leave the wall uncovered for a while, particularly through some bad weather if you can and see if the brickwork is damp.
If you're not having other condensation/mould problems in that room then opening the vents on the veluxes will probably suffice.
either batten or dot and dab again with insulated board.
Find the reason then fix that, of course you can always go belt and braces, and account for both damp and cold bridging, but there's extra cost involved

 

[Guyray]

Thanks. And what do I do if the brick work does prove to be damp?

With regards to re-dabbing it, I was planning to batten to minimise contact between board and wall, but does most insulated plasterboard have an inbuilt DMP?

Also, what would your belt and braces suggestion be? The room will be recarpeted and decorated so belt and braces is preferred!

Thanks again

 

[Guyray]

Gents,

Does the foil on the back of the insulated plasterboard serve as an adequate DPM to prevent any further bridging? If so I'd be happy with my builder's proposal to use dab again. Otherwise surely battening is the best route?

 

[roy c]

You cant dot and dab straight on to foil back plaster board. There is no suction on it...You may be able to sbr the back and throw sand on it but I have never heard of that being done. See what the "lads" say....I stuck polystyrene onto foil back with "Unibond" years ago then dot and dabbed them onto the walls....That was before you could get poly backed plaster boards!!

 

[chappers]

Thanks. And what do I do if the brick work does prove to be damp?

With regards to re-dabbing it, I was planning to batten to minimise contact between board and wall, but does most insulated plasterboard have an inbuilt DMP?

Also, what would your belt and braces suggestion be? The room will be recarpeted and decorated so belt and braces is preferred!

Thanks again

If damp find the source and fix it, it's a loft so would almost certainly be from a leak.
plasterboard insulated with celotex or similar would be impervious to damp due to the foil backing and plasterboard adhesive sticks to it fine.
Belt and braces would be to batten, and then use insulated board, as opposed to either batten and std board or insulated board and D&Das that wall appears to be cold wouldn't be a bad approach anyway. Battening with std board might still give you a cold bridge anyway and could still cause pattern staining.

 

[Guyray]

You cant dot and dab straight on to foil back plaster board. There is no suction on it...You may be able to sbr the back and throw sand on it but I have never heard of that being done. See what the "lads" say....I stuck polystyrene onto foil back with "Unibond" years ago then dot and dabbed them onto the walls....That was before you could get poly backed plaster boards!!

Thanks Roy C