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Condensation in Attic

  • 01-11-2013 4:35pm
    #1
    Registered Users Posts: 4,739 ✭✭✭ Zardoz


    I have a problem with condensation in my attic.
    There is often condensation on most of the North face of the roof ,the joists are often soaking wet too .

    The roof is almost bell shaped,it has 4 sides and no gable ,it is slated .
    From what I can see there is no venting in the slates or in the soffit.

    The soffit is wooden and nearly 30 years old ,it is in good condition on the East,West and South side but the paint keeps cracking on the North side.

    I stripped the wood down a few summers ago during a dry spell and primed it and painted it after it was bone dry,however it is cracking again.I suspect condensation on the inside of the wood is causing this cracking.

    The North side of the house ( 2 storey) is quite cold ,I dont have much heating on that side .

    I'm thinking that no venting in the soffit is bad and that I need to put some in and this may reduce the condensation ?
    I have read that one should have 1 square foot of venting for every 150 square feet of attic space ,is this the case in Ireland ?

    Perhaps some extra attic insulation could be of benefit,its old and probably not designed for our recent cold winters ?

    If anyone has some feedback it would be great ,many thanks


Comments

  • Moderators, Regional North West Moderators Posts: 43,204 Mod ✭✭✭✭ muffler


    Your attic clearly lacks ventilation which is essential and also given the level of condensation you are experiencing you really need to see to this ASAP together with providing heavier insulation to the ceiling.

    If its a standard attic (not dormer style house) then you need to ensure you achieve a minimum of 10mm wide strip ventilation to full length of soffits around house or the equivalent surface areas in fixed vents at equal spacings.


  • Moderators, Regional North West Moderators Posts: 43,204 Mod ✭✭✭✭ muffler


    Zardoz wrote: »
    I'm thinking that no venting in the soffit is bad and that I need to put some in and this may reduce the condensation ?
    I have read that one should have 1 square foot of venting for every 150 square feet of attic space ,is this the case in Ireland ?
    The regs can be viewed here


  • Registered Users Posts: 21,702 ✭✭✭✭ mickdw


    Insulate and ventilate. Also ensure there are no cooker / bathroom vents just venting to the attic space - Ive seen this many many times.


  • Registered Users Posts: 4,739 ✭✭✭ Zardoz


    muffler wrote: »
    Your attic clearly lacks ventilation which is essential and also given the level of condensation you are experiencing you really need to see to this ASAP together with providing heavier insulation to the ceiling.

    If its a standard attic (not dormer style house) then you need to ensure you achieve a minimum of 10mm wide strip ventilation to full length of soffits around house or the equivalent surface areas in fixed vents at equal spacings.

    Thanks Muffler for the detailed reply,much obliged.

    Its a standard attic yes ,the roof pitch is very steep and the attic space is very high .

    I dont understand why the house never had the ventilation strips installed when it was built 30 years ago.
    The attic space looks in excellent condition except for the condensation .
    Insulate and ventilate. Also ensure there are no cooker / bathroom vents just venting to the attic space - Ive seen this many many times.
    Thanks mickdw,I dont have any cooker or bathroom vents going into the attic as far as I am aware .

    Is it an easy job to install strip ventilation strips ,i.e diy or would I need a builder ?
    What thickness of insulation should I be looking at ?

    I'll have a chat with a friend of mine who is a builder and see what he would recommend.


  • Registered Users Posts: 4,739 ✭✭✭ Zardoz


    Update
    I think that there could be a leak in the North face of the roof .
    After the recent rain ,I noticed a few wet patches on the ceiling in a bedroom so I went up into the attic to investigate.

    This is what I found as shown in the 4 attached pictures.
    Alot of joists on the North face are wet from 4-5 feet down whilst the joists on the other 3 sides are fine.
    The insulation is damp in a number of places .

    Initially I thought the issue was condensation but perhaps it could be a leak but would so many joists be wet if it was indeed a leak ?
    The roof looks ok from the outside ,I cant see any missing slates or damaged slates.

    Many thanks


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  • Registered Users Posts: 2,202 ✭✭✭ jack of all


    You need to investigate a possible leak, perhaps wind driven rain finding it's way through a cracked or missing slate or tile or dislodged ridge tile. Don't upgrade the insulation until you have introduced adequate ventilation into the roof space. Make sure all water tanks are covered as an uncovered tank will produce a considerable amount of condensate. Seal/ make good around any penetrations in the ceiling (large holes around cables, pipes and light fittings, especially over bathrooms allow moisture laden air to enter the roof space). Provide vents in the soffit or if you intend to replace with pvc ensure that the existing soffits are removed or cut back before fitting. I've seen condensation problems in older houses like this where the original timber soffits and fascias were replaced with pvc. Timber would shrink over time and the small gaps and cracks which resulted were sufficient to allow the minimum ventilation required to avoid condensation, but when these are covered over with pvc problems can ensue if the vent grilles are obstructed. Make sure any insulation is pulled clear of vents and allow a minimum clear space of 50- 75mm over the insulation where it meets the sarking felt at the eaves to allow air to circulate over the insulation.


  • Moderators, Regional North West Moderators Posts: 43,204 Mod ✭✭✭✭ muffler


    When reading up on ventilation it says there should be inlet and outlet vents .
    I can put inlet holes in the soffit but I dont see how i can put outlet vents in the slate roof ,would the vents in the soffit be sufficient ?
    In theory, yes. Air should pass in through the soffit at the front and out the back or vice versa depending on wind direction.

    I have seen people put wall vents in the gable walls also which probably does no harm at all. The most important thing is to ensure a fairly continuous flow of air through the attic which will not only help with condensation issues but also prolong the life of your roof timbers.

    As pointed out by others insulating and draught proofing are essential when doing this.


  • Registered Users Posts: 2,292 RKQ


    I agree with jack of all above "Don't upgrade the insulation until you have introduced adequate ventilation into the roof space."

    Its been very wet and damp so condensation could be the cause but as we're had very high winds over a prolonged length of time I'd suggest wind driven rain is an issue.

    A gable wall vent won't work in your hipped roof but it is possible to get vent slates that can greatly improve cross-ventilation of your roof space. These vent slates can be installed near the ridge, allowing easier installation by a good Roofer.

    North Face Pic 3 could indicate loose or chipped slate - as water seems to be coming in thru the nailholes of the battens attached to joists


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