Water Damage to Ceiling — Condensation or Leak?

paperclap

Hi all,

In two corners of our bungalow, we've got black mould.

We have no cracked roof tiles, so don't think it's a leak from rainwater.

I have a sneaky suspicion it is condensation, and here's why.

In our loft, we have fibreglass insulation between our joists. We also have polystyrene insulation and board between our rafters. Above the areas where black mould has formed, the polystyrene insulation and board between the rafters has come away (I'm not sure how, though — maybe this does indicate a leak?). The roofing felt has also largely deteriorated in these areas, too. This, of course, leads to "cold spots" in an otherwise "warm loft". In turn, leading to condensation forming on the ceiling in the rooms, from the differentiation in temperature.

It is important to note that we've not experienced any more or less water in those areas after heavy rainfall. It seems to be around when condensation would typically form (on, for example, windows) — when the outside temperature is very low / moist (coldest days in the winter months).

We'll soon be having our whole house's ceiling plastered, so want to rectify this issue beforehand.

To rectify, I had planned to remove the roof tiles, patch up / replace the roofing felt and battens, and refit the internal polystyrene insulation and board.

Is my thinking correct, in that this is a condensation issue? What are everyone's thoughts?

Thank you in advance.

Jeepers_Creepers

A photo would really help - it's often very obvious what the cause is.

Who fitted the insulation and board to the rafters? Is it adequately ventilated up there?

grumbler

I don't think that missing insulation between rafters can create a 'cold spot in the ceiling underneath - especially if the latter is well insulated.

A leak is easy to detect - put a big plastic sheet underneath with raised sides.

paperclap

I've attached two photos.

I presume it was the previous owner of the house who fitted the insulation and boards, as it wasn't us.

When we had a HomeBuyers Report, it was noted that the loft was "poorly ventilated", and that the "polystyrene should be removed", but not in the same sentence / section. Never a reason as to why it was poorly ventilated, nor why the polystyrene should be removed.

grumbler

Looks like a leak to me (first photo). That said, it can be condensation on the felt dripping to the ceiling, to the leaking roof.

Jeepers_Creepers

Thanks for the photos.

Pic one - I suspect strongly that's water from above. It is too strong a stain and too well-defined to be condensation.

Pic two - hard to see the actual water mark, but if it's the long thin stain I think I see, then that too is, I suspect, water from above.

That is not to say it's from a roof 'leak', but more likely as a result of the poor ventilation mentioned in the report. There was another thread on here recently about the exact same issue and cause.

If your loft isn't well ventilated, then all the warm moist air from the house below percolates through into the roof where it cools and releases the contained moisture. This will condense out on the coldest surfaces first. This is likely to be the roofing boards that were fitted. The condensation gathers and starts to trickle down to the lowest part of the roof which is at the eaves. Here it drips onto the ceiling below...

Trying to insulate the 'roof' was a mistake. The roof space will always be colder than the house below, but that is not at all a problem provided the moisture that will get up there is ventilated away. You might think you want it 'warm' up there for storing things, but the best loft is one that's really draughty! Yes, it'll be bludy cold as well, but all your stored items will be bone dry.

All that polystyrene and boarding has done is to drastically reduce the overall ventilation up there = a condensation problem.

Could you take some photos of up there too? Including right into the eaves where the damp patches are.

paperclap

Thank you so much for the incredible insight.

So as such, it is condensation, but we’re seeing the after effects, or the tail end, of all our produced moisture?

I’ve attached some photos. 

One showing where the polystyrene and boards (and roofing felt) have come away. Incidentally, there actually is a “damp” looking spot on the ceiling plasterboard in the corner, which is the same size of that in the back room. I’ve not got a photo of the other area of the house (where the mould is visibly less prominent), but, from memory it is the same situation in the loft.

The other photos show where we’ve had issues with a damp purlin and a damp timber from the roof “web”. Now we’ve had marginally warmer weather (despite some rain), they’re both dry.

In the photos you can also see the style of polystyrene and boards.

Jeepers_Creepers

I think it's as you say.

That second photo is fascinating. Where the plasterboard has lifted at the bottom just above the purlin, a significant amount of water has clearly been running out from there. That can only been from one of two sources; a leak through the roof further up (unlikely if the tiles are all good) or condensation forming between the boards and the roof covering.

There should be a minimum of 50mm gap between any insulation or sheet and the underside of the roof AND this gap must be well ventilated, top and bottom.

If it isn't, you risk very serious long-term issues - it's called 'rot'...

I can't see what it's like along the bottom eaves - is there a gap leading out to the exterior soffits for ventilation?

paperclap

Jeepers_Creepers said:

There should be a minimum of 50mm gap between any insulation or sheet and the underside of the roof AND this gap must be well ventilated, top and bottom.

I've not measured... but don't think there is a 50mm gap between.

Jeepers_Creepers said:

I can't see what it's like along the bottom eaves - is there a gap leading out to the exterior soffits for ventilation?

We've got old soffits, so no purposeful ventilation system there either. A few splits / cracks (which ironically may act as ventilation), but nothing meaningful (such as a series of grills). They're next on the list to be replaced, but didn't suspect that being an issue really.

So, I guess we would do well to simply remove the polystyrene insulation and boards altogether then... and keep the fibreglass insulation between the joists?

FreeBear

laurencewhymark said: So, I guess we would do well to simply remove the polystyrene insulation and boards altogether then... and keep the fibreglass insulation between the joists?

Certainly remove the polystyrene and PB from the loft space. It is causing more problems than it solves.

Get some more fibreglass/rockwool insulation up there. Try to get it right under the eves without it touching the felt. You may need to get creative cutting the stuff to size and pushing it in to place with a broom handle.

Away from the eves, aim for a minimum of 270mm thickness of insulation - Shouldn't cost a fortune if you can do the work yourself (B&Q and Wickes have loft insulation on offer at the moment).

Jeepers_Creepers

laurencewhymark said:

We've got old soffits, so no purposeful ventilation system there either. A few splits / cracks (which ironically may act as ventilation), but nothing meaningful (such as a series of grills). They're next on the list to be replaced, but didn't suspect that being an issue really.

So, I guess we would do well to simply remove the polystyrene insulation and boards altogether then... and keep the fibreglass insulation between the joists?

Absolutely remove the boarding and insulation between the rafters - let that area breathe. Also, if that water is from an actual leak - say a loose ridge tile - then you want to know! At the moment it's all hidden.

Whoever fitted these boards thought there were doing the right thing - 'insulate the loft and it'll be warmer'. That 'warmth', however, has come from the house, along with a large amount of moisture. It then wasn't removed, but instead condensed out.  A loft should be cold and draughty! 'Cos then it'll also be dry :-)

As FB says, it looks as tho' you could increase the ceiling loft insulation up there - keep the heat where it belongs, in your house. Make sure your loft hatch is also insulated, and nicely sealed when shut - it should ideally have a foam seal all around it.

Don't tuck the insulation tight into the eaves, but leave a gap that leads out to the soffits. The new ones - when you come to replace them - should have continuous vent grills along its length.

Remember - cold and draughty!