Loft condensation –Airbricks perhaps?

[michael]

Is listed building consent, planning permission or building regs permission required to install air bricks on a grade 2 listed property? In my case two or three air bricks might be the way of allowing sufficient ventilation into a ‘lean to’ loft space which continues to suffer badly from condensation. Being on the side of a hill, the air bricks would be visible to the public on the other side of the wall that the roof is leaning against and would be located about head height to passersby albeit the foot traffic in this residential street is quite minimal.
There are no options for ventilation through the walls at either end of the 'lean to' roof as these would open up into occupied indoor spaces, one end of which is a party wall into my neighbor’s house.

The early 19th century design of this lean to roof doesn’t unfortunately allow eaves or soffit vents to be effectively installed and the tile (slate) vents currently installed also seem to be quite ineffective.
I looked at the loft insulation late last summer and doubled up on the thickness and blocked up any areas where I thought there might be warm air leakage into the loft but to no avail. Dripping rafters, dripping roofing felt and sodden loft insulation always returns at this time of year so I’m hoping overkill on the ventilation with air bricks through the wall that the roof is leaning against might solve the problem.

I suppose another alternative could be a wall mounted dehumidifier installed in the loft space but I'm wondering if the dripping condensation would make this an electrical/fire hazard? Does anybody know how to select the correct sized dehumidifier against the space to be dehumidified i.e. liters per day or however they’re sized? This also seems like quite an expensive option so the air brick solution would be preferable if there’s no LBC/planning complications.

 

[Penners]

Technically, I suppose this would require LBC. But I suspect (hope!) that a CO wouldn't stand in your way, or require a full LBC application for such a minor job.

Maybe a phone call or an email to your CO might be the best way to proceed - just a simple "would this be OK?" request. Give a brief explanation of the reasons why it's necessary ('improved conservation of the building' might be a useful phrase!).

Let us know how you get on.

 

[Roger H]

These vents were mentioned on a previous similar discussion: http://www.lapvent.co.uk/fitting-instructions.html

If I were your CO I'd want an LBC to formalise it.

 

[michael]

Hi Roger
As mentioned, the ‘lean to’ roof already has three lap vents (or tile/slate vents as I called them) which are proving ineffective probably due to the fact that it’s not really possible with the old roof design to back them up with eaves or soffit vents to create the draft. What I’m looking at is terracotta ‘air bricks’ venting to outside through the wall that the roof is leaning against.

 

[Lime]

My gut feeling is that you haven't sorted the ingress of warm moist air from the house entering the void.
To get the amount of water you describe in your loft must mean that water, in some form, is entering the space faster than the vents allow it out.

 

[DJH]

An essential requirement to prevent warm moist air from below entering an unheated cold roof space is a vapour barrier fitted preferably on the warm side of the insulation in a situation as you describe. By the fact that any barrier, such as polythene sheet, has to be both fixed in position it's self and will no doubt be pierced by the fixings required to hold up the ceiling covering below they cannot be relied upon to be entirely successful.

You say that there is no provision for any air vents or ducts at the eaves but I expect you could drill up through the wall at that position and fit some sort of pipes (plastic, copper perhaps?) up into the roof from there to introduce some air into the roof space provided they extend past the insulation. There is also a detail that can be fabricated from timber and lead which can be fitted at the head of the roof to form a continuous vent integrating the flashings there. I'll dig up a detail of it if I can find one.

Doug

 

[Roger H]

Thanks Michael. Understood.

Re Lime's comment - I've just unscrewed a ceiling rose and there was a fair sized hole in my ceiling that must have been sucking warm air up into our loft space. The hole is now masticked-up with a further bead of caulk around the perimeter of the cover, and a dab to seal the hole where the flex comes down through it.

 

[Lime]

Thanks Michael. Understood.

Re Lime's comment - I've just unscrewed a ceiling rose and there was a fair sized hole in my ceiling that must have been sucking warm air up into our loft space. The hole is now masticked-up with a further bead of caulk around the perimeter of the cover, and a dab to seal the hole where the flex comes down through it.

That is one of the most common warm air escape points.
Some others are via open top partition walls and via cracks and holes hidden behind fitted cornice.

 

[88v8]

Terracotta air bricks have a pretty small open area. As has been said, you need to stop the hot air getting up there. Another solution is to remove the roofing felt, or at least cut significant holes in it all over the roof so that air can percolate out through the gaps between the tiles.
I suppose you don't have any extractor fan trunking in the space that might be leaking warm/damp air?

Ivor

 

[Flyfisher]

Airbricks might have a pretty small open area, but isn't the point of them to allow air to circulate? A small, but constant, breeze flowing through an attic (or underneath a suspended floor) will do wonders for removing damp air (though I agree it's also helpful to prevent warm, humid air from entering an attic as much as possible).

Thus even a couple of small airbricks at each end of an attic at about eaves height, coupled with a few lapvents nearer the ridge, would - I'd expect - work wonders at keeping the attic dry and airy.

 

[Roger H]

Would some vertical ventilation slits be any good? (depending on local precedent). You also see claypipes used as vents in some places (meshed internally to keep out the fauna).

 

[andrew gayton]

my neighbour had a similar problem. we ventilated the roofdpace by opening up the laps in the felt and cutting a continuous slit under the ridge - you could do this against the top of the lean-to where the cover flash is (if I have understood correctly)?

my neighbour had been told by a roofer that the roof was leaking and had to be refelted; they looked quite shocked when I asked for a stanley knife.

A week later it was all good.

LBC would be required for the vents. Try the felt venting first.

 

[DJH]

I suppose firstly you don't want any warm air that you've paid to heat migrating up into an unheated space be it moist or not, and a vapour barrier is in my mind a must in situations like this. Where you fit this barrier retrospectively is difficult but a good start would be to remove the present insulation ( I'm assuming it's glass fibre) and lay a barrier over the ceiling joists and then replace the insulation.

An alternative method would be to insulate between the rafters with a rigid type insulation and tape, or mastic, any joints to prevent air meeting the cold underside of the roofing felt and condensing. There is of course no substitute for removing the slate/tiles and laying a breathable type covering on to the rafters, fixing a counter batten on each of the rafters and then slating or tiling on cross battens as normal. The idea here is that moist air which permeates the breather membrane is then ventilated away in the space created by the counter batten and, as the membrane doesn't allow water to pass back through it, any ingress of water is carried away to the eaves gutter.

Doug

 

[andrew gayton]

technically correct although an underdrawn ceiling with the insulation above will generally be adequate in stopping most of the heat loss. even a minimal amount of ventilation in the cold (er) roof space will have dramatic results. Thousands of roofspaces with retrofitted insulation work well if vented without the need to fit a vapour barrier.

 

[vicky whitworth]

A subject after my own heart... here's what we had to do to reduce the condensation in our loft. Loft already had two air bricks at each gable end.
Install lapvents towards the top of the roof on both sides. Remove the insulation that been stuff down the sloping roof sections which was preventing the gaps at the eaves working properly, seal up all the gaps between the warm cottage and the loft including three loft hatches that weren't used, put in loads of insulation on the floor of the loft. This entailed removing the pantiles half way up the roof on both sides because there was no other way to get the insulation stuffed down the slopes out, taking off the impermable roof felt while the tiles were off and replacing with breathable. Total cost including scaffolding all round £8k. And nothing to show for it except a dry roof - I hope. I've not looked since! Not a listed building though but from the outside no one would know anything had changed - you can't see the lapvents. Nightmare. Good luck with your problem. I hope it works out cheaper.

 

[andrew gayton]

laps in underfelt can be opened and vented via the use of small lengths of tile batten cut down the middle to a halfway point - to resemble a wooden clothes peg - then fixed into the lower felt lap to provide the vent.

 

[michael]

If you can imagine, this is a lean to roof so there is sufficient loft space to kneel upright close to the wall that the roof is leaning against but the loft space falls away rapidly on one side with the pitch of the roof.
Like Vicky, my ceiling below the loft runs flat throughout the rooms but drops to follow the pitch of the roof for the last 3ft or so towards the eaves.
That means that the loft space above that last three foot of ceiling towards the eaves (albeit about 25ft long) is only the depth of the rafters and like Vicky each of these shallow voids between the rafters has been stuffed with insulation.
In the last couple of days, with a bit of experimental drilling I’ve managed to install four small circular vents (70mmdia) in the soffits of a recessed window and recessed exterior door which are directly below the eaves of the lean to roof. This also meant dragging out the stuffed insulation from between the corresponding rafters with a makeshift pole and hook (dreadful, difficult and tiring work) but I think I now have a little eaves/soffit ventilation. The only problem with this I’m sure is that warm air will no doubt filter through the lath plaster ceiling where the insulation has been pulled out.(we’ll see)

I’ve also double checked the connections of the flexible plastic bathroom extract fan which runs in the loft to a lap vent. I’ve double taped up the connections at each end of the duct with silver ducting tape.

Another area where heat may be entering the loft is from under the 25ft x 3ft ply board loft crawlway which runs adjacent to the lean to wall. The ply is about 25mm thick and there is rock wall insulation between the ceiling joists under the ply but I should perhaps cover the top of the ply with insulation and roll it back only when access is necessary?

Any tips for sealing a loft hatch? Again my hatch is made of 25mm thick timber and sits in a timber frame within the ceiling joist structure. There are no hinges, it’s a fairly snug fit and it just pushes up into the loft. Last year I installed strips of fitted carpet in the hatch seating i.e. the hatch seals itself by sitting on the carpet within the frame and I also installed a secondary hinged plywood hatch above the existing timber hatch. This is connected by chain so that it pulls closed when the main hatch is lowered into its seating.

I’ll see how we get on but I may be looking at installing an additional lap vent and if that fails I’ll probably go for the air bricks as well.

Thanks for all for your suggestions.I'll try one thing at a time

 

[michael]

Could these polystyrene rafter insulation boards be a possible solution to my loft condensation problem?

http://www.wickes.co.uk/polystyrene-rafter-insulation-boards-pk3/invt/210020/

As one reviewer states: - “The panels have a series of very deep slots running along their length that are cut to match the panel to the width of the rafters. The remaining slots provide compressibility so the panel can be squeezed concertina-like between the rafters and the tension induced holds the panel firmly in place. No tape, glue. tacks or anything else required. A clever, neat, simple and effective design.”

It seems to me that with these panels ‘tightly’ installed between the rafters, there would be no cold slate or roofing felt surface for condensation to form on?

 

[MdB]

My guess is it wouldn't do much unless you completely changed the way the ventilation worked.

With a ventilated loft space, both side of the insulation would be cold.

 

[Lime]

Could these polystyrene rafter insulation boards be a possible solution to my loft condensation problem?

http://www.wickes.co.uk/polystyrene-rafter-insulation-boards-pk3/invt/210020/

As one reviewer states: - “The panels have a series of very deep slots running along their length that are cut to match the panel to the width of the rafters. The remaining slots provide compressibility so the panel can be squeezed concertina-like between the rafters and the tension induced holds the panel firmly in place. No tape, glue. tacks or anything else required. A clever, neat, simple and effective design.”

It seems to me that with these panels ‘tightly’ installed between the rafters, there would be no cold slate or roofing felt surface for condensation to form on?

To have condensation in a roof space there must be a source of moist air for the water to condense out of when cooled.
either the moist air is from outside (is the outside of the roof covered in condensation?) or from inside the house.

Fitting the insulation would not stop the water condensing out of the moist air if the roof space was still cold.
You may also introduce another area where condensation could form, ie between the slates and insulation.