Roof moisture solution

[Dylan T]

Hi all -

My house has a boarded loft space used for storage in my detached gable roofed house. Lately the condensation in there has been immense and is damaging all my stuff i've got stored there which has been gutting. The felt itself is really wet and dripping, while the rafters really look like they're getting damaged.

There are 2 vents in the north facing side of the house, which is also where the condensation is settling. One vent has the extractor fan for the bathroom below hooked up to it, so isn't providing ventilation to the loft itself.

The problem is, I've spoken to a couple of roofers and no one is willing to come over and have a look first, saying they are certain the problem is air flow and that I'll need extra vents, and want to book the job in first without first checking it out. I get not wanting to waste a trip, but I'm concerned that may not be the or at least the only problem.

I understand if there is condensation in the loft it will naturally condense on the coldest side of the roof (which is what is happening) but I don't understand how if a few more vents are added the water will naturally escape through here; isn't it inevitable that loads will still be condensing on the felt? They have also recommended two vents on each side of the roof - does that sound about right?

Many thanks!

 

[^woody^]

Ventilation is not so much to stop condensation, but to stop mould.

Preventing warm air getting into the loft reduces but wont completely stop condensation. Has your boarding of the loft has removed the insulation that would minimise the condensation?

 

[Leofric]

The generally accepted principles of good building construction for cold pitched roofs are thermal insulation at joist level, vapour barrier/check/control layer on the warm side of the insulation to reduce the risk of moisture laden warm air entering the roof space , and cross ventilation of the roof space.

 

[^woody^]

The generally accepted principles of good building construction for cold pitched roofs are thermal insulation at joist level, vapour barrier/check/control layer on the warm side of the insulation to reduce the risk of moisture laden warm air entering the roof space , and cross ventilation of the roof space.

Really? Accepted?

Hands up anyone who has a new house or extension or one built in the past 10,20,30 years or so that has a loft with a vapour barrier below the loft insulation.

 

[Leofric]

Hands up anyone who has a new house or extension or one built in the past 10,20,30 years or so that has a loft with a vapour barrier below the loft insulation.

Anybody with foil backed plasterboard

 

[martin hill]

Hi all -

My house has a boarded loft space used for storage in my detached gable roofed house. Lately the condensation in there has been immense and is damaging all my stuff i've got stored there which has been gutting. The felt itself is really wet and dripping, while the rafters really look like they're getting damaged.

There are 2 vents in the north facing side of the house, which is also where the condensation is settling. One vent has the extractor fan for the bathroom below hooked up to it, so isn't providing ventilation to the loft itself.

The problem is, I've spoken to a couple of roofers and no one is willing to come over and have a look first, saying they are certain the problem is air flow and that I'll need extra vents, and want to book the job in first without first checking it out. I get not wanting to waste a trip, but I'm concerned that may not be the or at least the only problem.

I understand if there is condensation in the loft it will naturally condense on the coldest side of the roof (which is what is happening) but I don't understand how if a few more vents are added the water will naturally escape through here; isn't it inevitable that loads will still be condensing on the felt? They have also recommended two vents on each side of the roof - does that sound about right?

Many thanks!

If your loft is well insulated it will get some condensation but should only be minor while it cold outside. If you have soffits with vents make sure the insulation around the edge isn't blocking the air flow. As Woody says it is rare that Vapour barrier on ceilings so best bet is to check no holes under ceiling roses and downlights sealed properly. The worse culpert for moisture getting into loft space is the bathroom or ill fitting loft hatch. Do you have a roofing membrane or the old roofing felt.

 

[Leofric]

Ventilation is not so much to stop condensation, but to stop mould.

- but mould is caused by excess moisture which can lead to condensation which can lead to mould. Inadequate ventilation can cause excess moisture. They are all related.

 

[^woody^]

- but mould is caused by excess moisture which can lead to condensation which can lead to mould. Inadequate ventilation can cause excess moisture. They are all related.

Yes mould and condensation are related, but it's not a direct reciprocal relation - ie one does not have to follow the other.

So on the basis that air will always contain moisture, and that condensation can't be prevented in a cold loft, ventilation is designed to deny the conditions for mould to develop.

 

[Leofric]

ventilation is designed to deny the conditions for mould to develop.

Yes, I agree with that. Don't know if we are splitting hairs here but ventilation also reduces the risk of condensation.