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Loft ventilation - Tips for ventilating your loft

Submitted by Richard

Lack of air flow in a loft space can lead to problems with condensation, which in turn can damage the timbers and the loft contents if not checked.

Line the loft floor with building paper (under the layers of insulation). This will prevent moist air from percolating through the ceiling plaster. Also add a draught strip around the hatch opening.

The loft space can be ventilated in a number of ways. Special vents are available for insertion into the soffits (the boards immediately under the fascia boards supporting the gutters). Or special tile vents can be found at a builders' merchants; these can be used to replace existing roof tiles-though the ideal time for this is during building or renovation of a roof. Ridge vents are also available.

Ventilation bricks can be inserted in end gable walls if this is more convenient. Add fine perforated zinc or other metal mesh to keep out wasps looking for nesting sites.

You can make your own vents by cutting holes in the soffit boards with a jigsaw, then covering the opening with a fine rustproof mesh. Add a simple quadrant beading to secure the mesh and make the job look neater.

Ensure that all vents are kept free of debris such as fallen leaves.

This tip has 14 comments shown below

Comments by: Gary from UK Dec 07, 2010
After the builders fitted a new roof and adding celotex between the rafters and plastered over, we had loads of condensation at eaves level and wet patches on the plasterboard.! we later found out that NO air vents were placed in the facia boards and no ridge vents (hence the condensation due to no air flow) We are now fitting our own vents on the facia boards (BETWEEN EVERY RAFTER) and adding 4 ridge vents in order to provide cross ventilation as well as vertical ventilation.
We dont have soffits due to it being a old house, so venting the facia boards at low level was our only sensible option, we are using the 70mm round vents as the photo above shows, this should cure our condensation problem with ease.

Condensation in loft resolved
Comments by: J Fletcher from Bournemouth, Dorset Jul 02, 2010
I had a problem with condensation in the loft, after some considerable time searching for the right
product I had lapVent installed by a local company. The installation took under an hour to complete, the results were almost immediate. It was the best £280.00 I have spent, I would recommend this product IT WORKS, unlike other imitations. I found it on the web, see below.

Other ventilation
Comments by: P Bywater from Bournemouth UK Mar 18, 2010
I have worked in the insulation industry for 15 years and there are many ways to ventilate the roof space, many of which have been mentioned, but one hasn't, there is a system called 'Easyvent' that is a spring loaded board that slips between the layers of felt in the roof, is inexpensive and seperates the layers of felt safely and allows fresh air to clear the problem, one should be fitted for every 6-8M2 of loft space and they are anything from £5 - £10 each, hope this helps as our installers use them all across Dorset, Devon and Hampshire and they are sold all over the country.

Loft condensation
Comments by: Jason from UK Feb 07, 2010
I have had significant problems with my loft since having my facia and soffits renovated, the guys who did the work did not fit the correct soffit, also i only had 50mm of insulation in my loft, thus heat was passing from my living space into the sealed loft space, then condensating on contact with colder materials.

I have fitted :-

300mm of insulation, inclusing loose lay insulation around the vertical timbers, insulation overlay loft hatch, and draft seal, if you have older house like me make sure you do not block perimeter air flow from vents.

Circular soffit vents, at v close centres, BC state min 250mm horizontal.

Had 2 ridge vents fitted also.

Part F.

Comments by: Anonymous from Not specified Jan 01, 2010
we have a plastic type felt under tiles and its raining in the loft with condensation. our house is 6 yr old and not sure if builder is responsable. we have been advised to insulate the rafters with kingspan insulation 100mm do you think this will stop condensation

Roof Tiles
Comments by: Gary James from UK Dec 29, 2009
I've got 'Jeff Capes Felt' which is plastic thus attracting more moisture in the cold. I don't have soffit vents as it's an old house and the roof meets directly with the walls.
I had two roof tile vents installed as well as two large Velux windows (vented at each side) at different levels.
I still have water running down the felt every morning and a line of water on my loft insulation in stages which drips throughout the day.
The condensation was present before the loft insulation was put in but it's a lot worse now.
Any tips would be greatly appreciated.

So many options!
Comments by: Andrew Harmsworth from Cambridge, England Dec 28, 2009
Very many thanks for the many tips - having insulated (to 30 cm deep) 60% of our loft, condensation levels have gone so high it virtually "rains" in the loft when it's cold outside. I'm clearly going to have to remove all the insulation and add some 'building paper' which will cost me more than the insulation itself. This set of tips would be even more helpful with pictures...

Roof ventilation
Comments by: Colin from Glasgow ,Scotland Jan 10, 2009
Good advice here for any roof cavity.
Ventilation is essential to carry away moisture that builds-up in the cavity and I know that it is an essential part of building regs for new homes in the UK. Which type you use can vary from the type available for the roof you have to the practical or aesthetically acceptable. Most modern timbers have protection from pests and spore damage, however, any build-up of moisture is going to create an unhealthy environment for the timbers and the occupants. Stagnant air is not a good thing. Look at all the options and decide which is the most effective, the most discreet, [ you don't want ridge tiles across a thatched roof!!] and sometimes the most expensive is not always the best. The advice given is very good for any home and venting your roof soffits may just be the answer. A word of caution, make sure the soffits are not made of asbestos before you go drilling or cutting. Check for stray old DIY cables and wasp nests first. Ouch! Good luck

Comments by: Ron Buttery from Devon, U.K. Jan 08, 2009
Good advice simply put. Would have welcomed more info on how to install vented roof tiles......what do you have to do to the roofing felt etc

Loft ventilation MORE
Comments by: George Katsarelis from Brighton, England Jan 05, 2009
Do I need any ventilation higher up the roof other than the soffit boards? I have been advised that I need a 10mm continuous vent in soffit boards and a 5mm higher towards the top of the roof. Is there any way to do this without having to resort to replacing tiles? cutting a hole in the roofing felt??

Comments by: Patrick McNamara from Wales UK Dec 23, 2008
I recently treated my loft for a woodworm problem (April) and all seemed fine. Eight weeks ago I went up to the loft and saw no problems. The weather since has been constantly wet and mist. I just came went up again and noticed that all the rafters and the undertile felt were wet. I don.t have any ventilation in the loft but will certainly be following your advice. Could it be that the large amount of water I used (mixed with Borax) never left the loft and is condensating? I have never had problems like this before ( the house is 130 years old and I have lived here for 8 years.

Looking for tips
Comments by: Tony from Suffolk. Dec 10, 2008
Thanks for the info, very helpful. I've just realised my place has no roof ventilation and I'm looking for all advice I can get before I carry out the work.

Loft Ventilation
Comments by: Anonymous from England Nov 09, 2008
Just want to say this website excellent. Will be visiting again. Several practical tips which to a novice like me are very useful.

Thanks for the tips
Comments by: Amy from USA Jul 23, 2008
Found the article very informative. Needing tips on ventilation...as well as heating and cooling a loft space. Thanks again.

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