Another one about condensation in lofts...

[amfisted]

The other day I happened to go into the loft, and noticed a small amount of condensation on the underside of the roofing felt. The space between the rafters is insulated, and judging by the dry moisture tracks on the underside of this insulation this is not a new problem. There's no sign of any rot in the timbers so presumably this problem only occurs in very cold weather.

I've read this forum's Wiki on this topic and a two part solution occurs to me. One, there's little air movement in the loft and the internal space at the roof edges is too limited to allow easy access to clear away any insulation or create new gaps, so I need to have roof vents fitted. Two, the bungalow has a concrete floor and all CH pipework enters the loft through the ceilings, so I need to make sure all those gaps are sealed, along with the loft hatch.

Is there anything else I should consider doing to help the situation? We have extractors in both bathroom and kitchen and the insulation on the loft floor, which is boarded over, is minimal, so I can't imagine that the loft is particularly cold.

Thanks.

 

[JohnD]

condensation on the underside of the roofing felt. The space between the rafters is insulated,

Don't understand that. Show us a photo please.

Also a pic of the eaves, in daylight (light should be visible through the gaps)

 

[amfisted]

The gap on the underside of the roof slopes between the rafters has been filled with insulation, though I'm not sure how it's held in place because it was here when we moved in. This is the blanket insulation that comes on a roll, and which is normally used on the loft floor between the joists.

I don't think the eaves admit any light during daylight, but I'll post a photo tomorrow as requested.

 

[JohnD]

so, starting from the outside, there are tiles, then felt, then mineral wool. Is that right?

 

[amfisted]

That's correct, yes.

Pictures now attached: first one shows insulation between rafters, t' other two the access to the inside edge of the roof space.

I suppose with a bit of crawling I could get in there to ascertain whether any additional ventilation is needed; and if so, how it might be created.

Asking some bod to come in and fit roof vents just seems somehow...easier, if costlier. Presumably and as long as it doesn't cause leaks or turn the loft into a wind tunnel, you can't have too much ventilation in a roof space?

That's correct, yes.

 

[John D v2.0]

That insulation is extremely odd, it looks like someone laid it on the rafters before the felt! And I'm guessing it's wet because there's too much humidity in the loft, so agreed that ventilation will help. Maybe you don't have any at the moment.

 

[amfisted]

The surveyor said when we bought this property in 2014 that putting insulation between rafters used to be a common practice, but is no longer considered efficient. However, it's not something I've ever seen before either, and this is the fourth home we've had with an accessible roof space.

I went up into the loft before, in daylight, then shut the hatch behind me and sat there in the pitch dark for at least five minutes to give my eyes time to acclimatise. However, not a chink of light from the eaves did I see.

Reckon I'll get someone in to quote for roof vents, so thanks again, Johns, for your assistance.

 

[amfisted]

Just to add that in the pics the insulation does look extremely wet, but it isn't. The darkening effect is probably the discolouration of age, and its only where the felt overlaps that there's a small amount of moisture.

 

[amfisted]

Revisiting this thread because I had a quote from a builder.

Roof vents were discussed, but gable vents decided upon as a less expensive alternative, coming in at a total of 200 quid for one in each opposing gable (detached bungalow). The soffits are closed, and we didn't discuss opening them up as an option.

Trouble is that the builder is very busy, and I have a feeling I won't be seeing him again for several months; possibly not before winter sets in and the condensation problem rears its ugly head again. Therefore I'm thinking about having a go myself.

I'm assuming its a matter of drilling through each loft gable wall using a core bit, fitting ducting through the brickwork and finishing off with terminals inside and out. I'd be installing static vents, not fan driven ones.

However, when it comes to buying the fittings themselves, most search engines point you towards American links. Could someone please signpost me to a UK supplier?

 

[John D v2.0]

You can get air bricks from any diy shop, just drill round a brick, knock it out (easier said than done) and mortar in the air brick.

 

[JohnD]

if you use a core drill, you can use round plastic ducts and grilles as used with bathroom extractors. It's possible to get a 100mm grill that can be inserted from inside the building, but results will be better if you work from outside. This will also cut the bricks more neatly without spalling. It is not safe to use a core drill off a ladder. I'd guess you'll need at least two holes at each end. You can get a cowl vent (pull the non-return flap out) if the wall is subject to driving rain, otherwise just drill so the duct is at a slight angle to drain outside.

It's possible that there is more than one builder in Flintshire, and the other one might own a scaffold tower.

http://www.screwfix.com/c/heating-p...40496?cm_sp=managedredirect-_-hvac-_-airvents
don't get flap vents, you want an open grille.

Duct is also widely available in 125mm and 150mm, and, less common, in bigger sizes. I have only used core drills in 100/110mm.

Core drilling is fairly easy if you have a firm footing and an overload clutch, and makes a neat hole (except on the other side).

 

[amfisted]

Thanks, John, not least for adding the advice that there might be "more than one builder in Flintshire". I'm sure there are indeed many, but the chap who gave me the quote has done good work for me before and is highly thought of locally. His prices are also very reasonable. I would only use someone else if I couldn't do the job myself; and in this case, I think I can.

I reckon I can use a core drill from a ladder; much of my professional life involved working at heights, often from ladders. However, your warning is appreciated and I will take care.

So..open grill. Is it worth adding a flyscreen? Obviously with the open eaves in old houses (such as the Victorian semi I lived in prior to moving here) ensuring the total exclusion of flying intruders can involve significant work. With my loft already being hermetically sealed, there would only be one easy route for insects into the roof space from outside and that would be through the new vents. We do already have an occasional issue with mason bees, and I don't want to encourage any further invasions. Spiders are always welcome as they keep other pests in check.

Thanks again for the advice and the link; much appreciated. And thanks also to t'other John for the suggestion about airbricks.

I only asked for a link because I thought there might be a specific fitting for ventilating a loft through the gable. Reassuring to know that I can use the kind of inexpensive grille that I've used before.

 

[JohnD]

you can get grilles with a fine plastic gauze, but I suspect they would soon clog with dust and cobwebs.

flies like to stay in the light, rather than going into dark places. If you ever get cluster flies, reconsider.

If you hire a big core drill, get one with a safety clutch and turn it as low as you can. If a core jams in the wall, it can whirl the drill, and the operator, round. There is a lot of torque.

 

[amfisted]

I suppose I could fit a screen on the inside of each vent and simply clean it every time I go into the loft.

I understand the point about torque with a core drill. I used one when fitting an extractor fan in the bathroom, and yes, there is huge kickback if they get stuck.

Thanks again.

 

[John D v2.0]

If you're really going to work up a ladder using power tools, first drill a hole to fit a hook, and tie the ladder securely at the top(so you can't move it with all your weight). Same goes at the bottom, make sure the base is firmly tied down and wedged. If you can strap yourself to the ladder too then that's good.
You only get one back/pair of legs/head so don't drop them from a great height!