condensation

johnnyb6

Hi I converted my attic few years ago and since then the felt is constantly weeping on frosty weather. I had engineer look at and he advised me to fit ten vents in roof. 5 in front and 5 in back. However the problem wasnt sorted. I put insulation on ceiling of attic room when I was converting it and I wondering do I need to remove this. It will result in attic been very cold then.

Thanking You:)

muffler

Have you sloping ceilings and did you insulate those? If so what type of insulation was used?

johnnyb6

muffler wrote: »

Have you sloping ceilings and did you insulate those? If so what type of insulation was used?

Yes I have sloping ceilings front and back. However front of house rarely weeps. I have rock wool insulation on sloping ceilings and i used netting to keep it in place. I have the 4 ordinary circular vents on the sofit. These are about 3 inches in width

muffler

The main issue would probably be the lack of through ventilation. Have you a 50mm gap between the rockwool and the felt along the sloping ceiling?

johnnyb6

In parts of it I have but the majority of it isnt. When I was securing the rock wool I tied it rather close to froof as I knew it shrinks alot over time. If i put more vents in fashia would that be any benefit

muffler

Go to page 28 of Technical Guidance Document F for details to show how the attic should be ventilated.

Adding extra vents to the soffit wont help if the air flow is being obstructed behind the sloping ceiling. The air needs to move in from the soffit and up and under the felt and out at or near the ridge.

johnnyb6

The engineer which looked at it for me said same, thats why I had to put 10 vents in. However most of my condensation is towards the facia at back of house. usually between facia and 2 feet up

Merch

did you use a breathable membrane before putting up the insulation?
I've looked into this only a little bit as I considered doing a part conversion for storage.

If there was a breathable membrane, it would still require the ventilation gap to be of an adequate size (50 or so mm), plus depending on the length (or area?) of the roof a certain number of vents of a certain dimension. check part L also, http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1647,en.pdf at about page 48.

It does show images of pitched roofing with counter battening, using both a breathable membrane and a vapour control layer (VCL).
and
what appears to be, without counter battening, using only a VCL.
Counter battening is when from my reading and putting up a tiled shed roof, is when the horizontal battens are raised off the felt by another vertical (top to bottom direction) up and down the pitched section of the roof.

I would hazard a guess that most roofs are not counter battened, while Id hazard a guess at the benefits of counter battening, I'm not certain when the limits of recommendation start. However, you will not be changing that.

Personally, I'd have thought a breathable membrane above the insulation to allow excess moisture out while limiting the ingress of moisture, combined with a vapour control/check layer to prevent moisture getting into that space, would be the ideal method. Again, if the space is in normal usage then there will also have to be ventilation into that space also.

Does the back of the house point towards North? as a non expert opinion, If it is the cooler side then it would suggest to me that warm/er air containing moisture from inside the house (which has the ability to contain more moisture) is condensing on the cooler portion of the roof. Which also suggests to me that the insulation isn't working somehow.
If there was adequate ventilation space between the felt and the insulation then this may be solved but it still doesn't solve that a cool exterior surface is still being (must be?) experienced inside.

johnnyb6

so should i try and fit new rig tiles with vents, or take down insulation

BryanF

johnnyb6 wrote: »

so should i try and fit new rig tiles with vents, or take down insulation

Listen to the mufflalater
It's tough but get over the shock..
Take down the plasterboard & insulation. Reinstall with 50mm gap between felt an insulation + allowing means of venting either at eaves or slate vents, re-insulate with appropriate insulation, fir out joists if required, then add vapour membrane/ air-tightness, then plasterboard.
This has been building regs for 15 years+?!!

Merch

BryanF wrote: »

Listen to the mufflalater
It's tough but get over the shock..
Take down the plasterboard & insulation. Reinstall with 50mm gap between felt an insulation + allowing means of venting either at eaves or slate vents, re-insulate with appropriate insulation, fir out joists if required, then add vapour membrane/ air-tightness, then plasterboard.
This has been building regs for 15 years+?!!

I'm not an expert OP so I wouldn't want to have given this advice, but it is what I would consider necessary by the sound of what you have said.

BryanF, I've read through part F, I just had a quick look over it there now,

When you say fit out joists, you mean build them up to account for the ventilation gap,insulation thickness and to support the plasterboard?
This something I have been considering doing to hold insulation and plasterboard, do you connect new beams to the whole structure and joined to the existing ones using noggins?
Part L, (pg 49) suggests only using breatheable membrane outside the insulation in a counter battened scenario, I'd have thought this is useful in any construction method, to allow any moisture that may get through a VCL to escape without letting new moisture in, mostly to maintain the integrity of the insulation but also as a means to prevent heat loss when ventilating that 50mm space between the tiles and breathable layer by convection.

Also, will the Op (or anyone doing this) have adequate ventilation in the space if only vents are fitted in the soffits?, the last images on page 29 of Part F, show typical possible construction cross sections of an attic space and both show a continuous vent strip at the apex. Would vents in the soffit on each side be sufficient?
or
would extra vent tiles near the apex be required, by removing a number of tiles and replacing with vent type tiles?, I cant see what dimension for the vents is required in Part F,

johnnyb6

In total shock now.Will still seek cheaper option

Merch

johnnyb6 wrote: »

Hi I converted my attic few years ago and since then the felt is constantly weeping on frosty weather. I had engineer look at and he advised me to fit ten vents in roof. 5 in front and 5 in back. However the problem wasnt sorted. I put insulation on ceiling of attic room when I was converting it and I wondering do I need to remove this. It will result in attic been very cold then.

Thanking You:)

when you say the felt is weeping, you mean there is condensation on the felt? how do you know if its covered in insulation?
Is it soaking through and creating damp patches?

archtech

johnnyb6 wrote: »

In total shock now.Will still seek cheaper option

That is the cheaper option . The expensive one would be having to remove the roof and replace it due to rotten timbers .

BryanF

archtech wrote: »

That is the cheaper option . The expensive one would be having to remove the roof and replace it due to rotten timbers .

+1
Johnny,
I here this all the time whether its dormer drafts, lack of insulation or roof ventilation. You've been given the solution. good luck to you

BryanF

Merch wrote: »

I'm not an expert OP so I wouldn't want to have given this advice, but it is what I would consider necessary by the sound of what you have said.

BryanF, I've read through part F, I just had a quick look over it there now,

When you say fit out joists, you mean build them up to account for the ventilation gap,insulation thickness and to support the plasterboard?
This something I have been considering doing to hold insulation and plasterboard, do you connect new beams to the whole structure and joined to the existing ones using noggins?

yes

Part L, (pg 49) suggests only using breatheable membrane outside the insulation in a counter battened scenario, I'd have thought this is useful in any construction method, to allow any moisture that may get through a VCL to escape without letting new moisture in, mostly to maintain the integrity of the insulation but also as a means to prevent heat loss when ventilating that 50mm space between the tiles and breathable layer by convection.

Also, will the Op (or anyone doing this) have adequate ventilation in the space if only vents are fitted in the soffits?, the last images on page 29 of Part F, show typical possible construction cross sections of an attic space and both show a continuous vent strip at the apex. Would vents in the soffit on each side be sufficient?
or
would extra vent tiles near the apex be required, by removing a number of tiles and replacing with vent type tiles?, I cant see what dimension for the vents is required in Part F,

vent tiles perhaps, it's site specific. Manufacturers will offer opinion on amount

holdfast

I have a similar story,but no weeping. I was away when my conversion for a room in roof was completed over 4 years ago. Just to say I have about 4 ft of rafter with no 50mm gap. There is breathable membrane and intello membrane on the inside with 200mm rockwool and 37mm kingspan. As there are void behind the knee walls and at the apex of the roof allowing some ventilation to the roof members in these locations, it is something I have been worried about the possibility of dry/wet rot.

I think I might inspect the roof members in the summer by stripping the slates and reveling the rafters. What do you guys think ? cheers

Poor Uncle Tom

holdfast wrote: »

Just to say I have about 4 ft of rafter with no 50mm gap.

You're aware you have no through ventilation and that you are in contravention of the building regulations.

holdfast wrote: »

I think I might inspect the roof members in the summer by stripping the slates and reveling the rafters.

That's nonsense, you already know you have the problem, the solution is to fix it from the inside, not the outside.

Remove the plasterboard finish, remove the insulation, add firring pieces to the affected areas, correctly position adequate insulation, slab, skim and paint.

Merch

holdfast wrote: »

I have a similar story,but no weeping. I was away when my conversion for a room in roof was completed over 4 years ago. Just to say I have about 4 ft of rafter with no 50mm gap. There is breathable membrane and intello membrane on the inside with 200mm rockwool and 37mm kingspan. As there are void behind the knee walls and at the apex of the roof allowing some ventilation to the roof members in these locations, it is something I have been worried about the possibility of dry/wet rot.

I think I might inspect the roof members in the summer by stripping the slates and reveling the rafters. What do you guys think ? cheers

Are you certain there is no gap? how do you know if you weren't there when it was installed, is that what the installers told you?? being curious not critical.

I keep saying, Im not an expert before I give my opinion, but these are the reasons and concerns about why I decided against doing a conversion, after I read up on different parts of the regulations, there are some very simple things that can be done at the time of the job, either the people doing the jobs dont know or dont care, I think its a mix of both in order to get the job done quickly.
But to retrofit the job to have it done right costs money, probably the same as it cost to put up, better to get it done right first time. I know its too late for those homeowners that either dont know or have the time to check it up, being heavily reliant on someone you are uncertain of their experience in the job is tough and I suppose some people just put their hands up and say, what can I do? (maybe?).
As an example, house across from my backgarden has a conversion done, in the frost and snow, their roof is either melted first or doesnt get frosted.Thats a seperate issue I know, but its a cause for concern what people that are doing conversions are up to! do they even read the regs.

Which leads me to an even bigger concern, when doing the work, are they affecting the integrity of the roof structure, particularily if its of prefabricated truss construction.

I would rather not get this done than have it done wrong.

I feel like more of an expert and from a practical point of view, how will you get under the felt? without damaging it! or doing more harm than good.
Whether you are certain or not of the gap, surely the best way to check will be to rip the inside out to check the condition of the beams and to determine if there is adequete ventilation space.

I dont like doing it but sometimes you need to look over peoples shoulder to make sure they are doing the job right or even at all, but in a job this big, its a given.

holdfast

Thanks for the replies. Yea, I know it against the building regs. I am pretty sure that is the case and there is no gap but never 100%. I know I have a problem, but how much of a problem is the question. I know I am grasping a straws but with the battens standing off the rafters this should allow the timber to breadth to some respect through the breathable membrane, fingers crossed. I am going to look at three lengths of rafter on the north side of the roof in the summer. I am going to take that action, beacuse I have over 1200 sq ft up there to strip if I have too.