Roof space ventilation in lofts and attics.


Postby Bus Godden » Thu Jun 21, 2007 5:52 pm

Nowadays our built environment has never been so ‘airtight’, double glazing, drought proofing, all sorts of insulation, etc. We are virtually ‘hermetically sealed in’ in many cases! It can’t be healthy, not for our buildings and certainly not for those who live and work in them.

As warm moist air rises it makes lofts and attics the last barrier to atmosphere and any kind of fresh air. Are we wise to ignore this growing area of concern? What are your thoughts on ‘roof space ventilation’?

Bus
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Postby htg engineer » Sat Jun 23, 2007 2:54 pm

Roof spaces should be ventilated, this prevents the build up of condensation off heat from the house, water vapour from the shower and bath's etc and also any water storage tanks in the loft space (should be fitted with a lid)

Air bricks are quite often covered up when loft insulation is laid, the loft insulation should not fit right into the eaves of a roof there should be a gap to allow for air circulation.

Roof vents can be fitted in place of roof tiles or slates. Houses with gable ends will have air bricks in the gable.

All vents and airbricks should be kept clear of loft insulation and stored belongings. And where's there's no vents they should be installed.

hope this helps
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Postby Bus Godden » Thu Jun 28, 2007 6:40 pm

Yes, thanks, your post covers things nicely but it is an area that’s rarely even fleetingly considered in the main as far as I can see - if things begin to rot in an attic it’s usually accepted as quite natural and dank airless conditions are generally taken as the norm (I’ve been guilty of it).

That should not be the case though because roof spaces would not smell and breed decay if adequately ventilated - a musty odour is not just stagnant air; it is the smell of airborne spore from destructive fungus, mildew, wet or dry rot, or some other sort of decay.

As you say roof spaces should be ventilated but they rarely are these days, at least not as well as they should be. Modern methods of building, new-build as well as refurbishment and repair, do not always address this problem, not anywhere near thoroughly enough anyway.

I’ve recently fitted a few Lapvent units inside, under my parent’s roof and they are just the job, but it’s a bit too late for some of the old family paraphernalia that was kept up there - hindsight and all that.

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Postby horsenut » Tue Jul 17, 2007 8:38 pm

Good topic, ive just had a scare with wooden soffits falling from my kitchen extension. After inspecting the soffit section i found it was rotten with fungus due to lack of ventilation. The extension was built in the 80s and im amazed to think we were not that advanced back then to realise the problems caused due to lack of ventilation.
Bus have you ever used a felt support tray, is it any good?
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Postby DONFRAMAC » Wed Jul 18, 2007 12:27 am

For 3 months in 1999, I sold double-glazing products,etc. I, myself, had purchased the roof-line products from the firm.
After my first sale, which included roof-line products, the customer complained that his upstairs rooms in his bungalow had become chilly. This was indeed true ;--- the soffit panels had far too many parallel vent slots. The manufacturer solved the problem by returning to 3-inch dia. vent inserts every metre, cheap and chearful. My own loft remains chilly.
MORAL : YOU CAN GET TOO MUCH OF A GOOD THING !
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Postby Bus Godden » Wed Jul 18, 2007 9:45 am

A ‘Felt Support Tray’ props up a run of roofing underfelt as it passes over the upper edge of the facia board at eaves level. During the normal run of things, any storm driven rain/snow that is blown between the tiles/slates, will eventually find its way down the felt to the lower reaches at the eaves (and hopefully into gutters!). If ‘unsupported’, it will usually sag below the upper edge of the facia allowing water to pool, and ‘Sods-Law’ says that in this instance, un-evaporated water will eventually find and destroy something vulnerable somewhere! (maybe ‘soffits’?)

Some Support Trays also stand off the facia board to provide a continuous ventilation gap - which is great for the immediate facia or eaves box areas. However, with the majority of buildings, there is no clear interconnection with the facia/eaves box areas and interior roof spaces; although some new-build projects do include ‘Rafter Trays’ to counteract this. The ‘rafter’ type of tray is supposed to introduce an end to end airflow through the bays formed between two side by side rafters, but often it doesn’t because of some kind of obstruction or other.

Are facia vents, soffit vents any good?

They certainly are, but only if they can do the job they are supposed to do!

A negative point; these systems rarely work on older buildings where they can be a bit of a con ('nothing' can get over the wall-plate!)! Furthermore, although ‘lower ventilation’ in a roof-space is of course necessary, it wont be entirely effective without some ‘upper ventilation’ in support – because warm, moist air, as we all know, ‘rises’!

[u]Horsenut[/u], at a guess, I would say that your soffit problem may have stemmed from a steady soaking of rainwater, rather than actual condensation. I could be wrong but it is worth further investigation – has any rainwater that has found its way under the slates/tiles been able to run off the felt underlay into the guttering?

[u]Donframac[/u], you have obviously experienced the reverse, probably on new-build where a clear run over the wall-plate is inbuilt through modern design (a response to the recent awareness of the problems that can be caused by hermetically sealing ourselves into our built environment). The judicious application of an external strip of very adhesive tape could well adjust the amount of airflow.

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