Loft conversion interstitial condensation problem

[Noidea1123]

Hi all. Recently, I found out that my loft has interstitial condensation. Our first step was to remove the insulation on either side; one side is nearly done.It is insulated halfway up on both sides. The problem is that there is a noggin between each pair of rafters, situated just before the pitched plasterboard meets the central boards, which run down the centre, which is visible from inside the eaves, looking up the inside of the pitch of the roof.

The house is from approximately the 1930's and the felt needs to be repaired in places. I'm happy for the room to be used as a loft rather than a bedroom in order to facilitate a quicker repair (it is going to be rented in August).

Does anyone have any ideas how to open up the structure for airflow, without ripping all of the boards out?
And... Can I leave the noggins in- or are they likely to be blocking airflow just like the insulation which is rammed in? Please see the photos attached, I welcome any advice. Thank you.

 

[freddiemercurystwin]

How do you know there is interstitial condensation? Is the insulation damp?

 

[JohnD]

I suppose this condensation is in fibreglass insulation? How do you know it is not leaks?

did the conversion have building regs approval?

Where do you suppose the water vapour is coming from?

 

[Noidea1123]

Hi, yes, glass fibre type, which was just packed into the upper half of the roof with no space for ventilation. We think the water is coming from vapour changing to water as it hits the cold inside of the felt and then running down the woodwork. There is evidence of water in the main beams that run lengthways either side. My idea is to remove the insulation (part done) to allow air to circulate- but this might be scuppered now we've noticed the noggins.

It didn't have building regs either. I want to return it to being just a loft and want to preserve the structure.

 

[JohnD]

It didn't have building regs either. I want to return it to being just a loft and want to preserve the structure.

In that case, pull off the plasterboard and the insulation, and open up eaves ventilation.

If you decide to do a proper conversion later, you can do it properly. You can leave the floor and lighting which may be useful.

Next time it needs a new roof, use breathable membrane instead of felt.

BTW if it is the old yellow fibreglass, i strongly advise a dust respirator, goggles, balaclava and overalls that you can strip off on exiting the loft. Use a builders vac with cartridge filter for the dust, and bag up the old material before carrying it down through the house. Loft dust with yellow fibreglass can be very irritant.

 

[Noidea1123]

How do you know there is interstitial condensation? Is the insulation damp?

Hi, a surveyor picked up on some black mould on some areas of plasterboard and water marks in the main lengthwise beams on left and right side. It's not that bad, as the insulation wasn't damp and the mould wasn't that extensive, but I want to make it good in terms of ventilation, preferably without stripping all of the plasterboard out (the loft has central heating and spotlights down the centre).

 

[JohnD]

preferably without stripping all of the plasterboard out (the loft has central heating and spotlights down the centre).

but you said you wanted to revert to a loft.

 

[Noidea1123]

I'm looking for a cost effective way to protect the building. I don't want to use it as a living space. We were just going to remove all the insulation with as little removal of plasterboard as poss, but this was hindered when we found each pair of rafters has a noggin at the top- which presumably would affect ventilation. Sorry if I wasn't clear.

 

[^woody^]

1. Deal with any excess humidity that is created within the room or other rooms.

2. Prevent moisture from penetrating the roof structure - barrier paint.

There is no need to open up the roof.

 

[RandomGrinch]

2. Prevent moisture from penetrating the roof structure - barrier paint.

(the loft has central heating and spotlights down the centre).

Creating an adequate vapour barrier over the spotlights may be a good start.

 

[Noidea1123]

1. Deal with any excess humidity that is created within the room or other rooms.

2. Prevent moisture from penetrating the roof structure - barrier paint.

There is no need to open up the roof.

Thank you for taking the time. Bear with me... Can I use vapour barrier paint on the plasterboard ceiling? I can't access above the spotlights without taking the ceiling out. On the right-hand side I have removed most of the yellow fibreglass insulation, which was thoroughly packed in, as we thought we needed to let the air flow. The plan was then to leave it without insulation and not to use it as a bedroom. (The floor is insulated to some degree).

 

[^woody^]

Are you sure the diagnosis was correct? What month was the survey?

Mould on the plasterboard is a room-side condensation issue requiring remedy within the room, and is evidence of a cold roof requiring more insulation and not [cold] ventilation.

Water on roof timbers is not in itself a condensation issue that needs a remedy, as it is common in extreme weather a few weeks a year.

Has a roof leak been totally discounted?

You really should not remove insulation and make the roof colder. That is a recipe for more condensation issues.

Yes you can use a barrier paint, gloss paint or an anti condensation type paint as that's the same thing.

You can get sealed spot light fittings.

Incidentally, be wary about letting a property with unauthorised (ie unlawful) building works.

Returning the room to a loft requires major deconversion work - plasterboard stripped, electrics removed, stairs removed.

 

[Noidea1123]

The survey was done in early May. She spotted the bits of external mould and water marks in the main beams and told our buyer not to buy the house. A leak hasn't been discounted and we have found one or two holes in the felt in the lower right portion which wasn't insulated-- below the beam.

The feedback from this survey is why we took it off the market and decided to rent it from the 1st of August. We get the keys to a new build on Friday and are prepared to forego a month's income from the current house to get it somewhere near right. It's been a nightmare.

 

[JohnD]

Returning the room to a loft requires major deconversion work - plasterboard stripped, electrics removed, stairs removed.

If there are no fixed stairs, it is not considered a conversion. You can have lights, sockets and a floor in a storage loft if you want. I don't think plasterboard matters, although in this case it is probably related to the damp spots, whether they were caused by leaks or condensation, so I favour removing it and the rafter insulation to see what's going on..

 

[Noidea1123]

Yep, no fixed stairs. If we end up stripping it, it wouldn't be cost or time-effective to reinsulate and board again at this point, so it's a big decision.