Mould growing on things in new loft

[Michaelsf90]

If the felt is breathable the condensation shouldn't be that bad. I have a similar issue. I insulated the loft to the required standard and it caused condensation. I used felt lap vents and they do work but you have to be careful of wind uplift. It's hard to find advice on lap vents. But your suppose to install them as close to the eaves as possible. In every other stud kind of thing. Also install a couple further up from the eaves, closer to the top. Don't install them directly opposite either or the wind will just blow straight through and won't circulate. Ideally you probably need some kind of roof ventilation like me. Once the weather gets better I'll be getting three roof tile vents at the bottom and two at the top on each side. Hope this helps

 

[Michaelsf90]

https://manthorpebuildingproducts.co.uk/product/g630-felt-lap-vent

Just scroll down and the installation instructions are in a pdf

 

[JP_]

Those are the Felt Lap Vents i bought

 

[Michaelsf90]

Have they worked? The vents helped for me but haven't cured it completely. I would say proper tile vents is a better more permanent fix. For me the lap vents where just to see me through this winter. Youd be surprised not many roofers have heard of lap vents

 

[Leofric]

'The specifier should ensure that the opening of felt laps on the property will not adversely increase the wind uplift load on the tiles/slates or the driving rain resistance of the roof '- quote from Manthorpe literature. So how do you do that ?

 

[Michaelsf90]

I suppose you'd have to ask a roofer or an architect? Someone with that kind of expertise. The fact roofers haven't really heard of lap vents says it's all to me. That it isn't a permanent fix. Only temporary. I've had my vents in for a good few months and we've had some bad gale force winds and my roof is still intact

 

[Leofric]

Why would you ask an architect ? I haven't known architects specify these things ,and as you say it sounds like roofers don't use them ! I would ask Manthorpe , they are selling them. How does anybody ' ensure that the opening of felt laps on the property will not adversely increase the wind uplift load on the tiles/slates or the driving rain resistance of the roof ' ?

 

[Michaelsf90]

I have heard of building control to specify them being used when loft insulation has been topped up. Architects have a wide range of building knowledge usually. The wind thing I'm sure has got something to do with wind direction and strength. Someone will know the info, but like I said a more permanent job is proper roof tile vents

 

[Leofric]

It isn't the job of building control to design buildings and specify materials etc - their job is to check that details submitted by others comply with building regulations. Of course architects specialise in building design but that does not mean they approve of every building technique that companies promote or DIY enthusiasts use. A more 'permanent' proper means of ventilating a roof space is to use breathable underlay supplemented by eaves ventilation to Approved Document details and an air brick at high level in a gable wall if possible. Roof tile vents would not normally be the preferred option. Ridge tile vents may be required in certain circumstances.

 

[noseall]

The fact roofers haven't really heard of lap vents says it's all to me

DIY retro' fixes are not high on any roofers list, lol. They tend to have heard of things like over-fascia vents or soffit vents, the likes of which are the correct installation during the building process.

These are usually installed by the chippy in any case. Roofers can't legislate for idiot insulation installers either.

Please don't criticise roofers when you don't know what you are talking about.

 

[JP_]

Regarding uplift, I reckon it's a case of fix them and see. I have some spare tiles. Don't really see how they could create enough uplift to move tiles and battens enough to cause any problems though.

So far, the loft is condensation free (apart from a couple of areas that might still be drying out - and I can put more vents in there too.

But the weather has been on my side - humid but warm enough, temperature generally above the dew point. In for some cold weather soon though so no doubt it will be tested.
It certainly feels fresher up there.

 

[Michaelsf90]

I'm not criticising roofers I'm saying for me the fact they haven't heard of them shows they aren't a permanent fix. Not a proper job so to speak. I've used the vents myself and it's greatly helped the condensation in my loft. It hasn't gone completely but it's 99% better so the lap vents do work and help. But once the weather is better and I have the money I will be getting proper ventilation. All I'm saying is lap vents do work and help and its up to the OP what they do but me personally I would want a proper job doing eventually