10 x Felt Lap Vents Prevents Loft roof Condensation. Attic Space Ventilation

Product Information

Danelaw® offers a wide range of roofing ventilation products covering a wide range of tile types and construction details, from new build developments to refurbishment.

Normal air gets warm and rises. It filters through the ceiling, getting warmer as it passes through warm rooms and eventually gets into the loft. The loft is usually colder than the house rooms and as soon as the rising warm air hits a colder surface the vapour immediately turns to water. This should be clear of insulation (or anything else for that matter) so that air can flow up into the loft space, circulate and then out the other side removing any moisture by cooling warm air down before it hits a cold surface. Add Vent Tiles or Ridge Vents. This is more involved as you will need access to the roof from outside, and this might need scaffolding, or certainly ladders. One (or possibly more) of the roof tiles is replaced with a vent tile which, as the name suggested has a vent in it to allow air to rise out through it I'm thinking I need to sort this out before I make the attic even colder with the extra insulation. Would felt lap vents like these: The lap vent is another easy solution for ventilation problems. Especially in poorly vented areas of the property. Though commonly used on older roofs with bitumen sarking felt (waterproofing layers), they can also be fitted to roof membranes if needed.

How to Ventilate a Loft or Attic to Prevent Condensation

The product has been designed as a remedial solution to help overcome the build-up of condensation in the roof space, however like all products that open the felt lap to provide ventilation it does not meet the code of practice BS 5534:2014+A2:2018 6.2.1.1. The specifier or user should be aware that the opening of felt laps on the roof may adversely affect the driving rain resistance of the slates, tiles or shingles, as well as increase the wind uplift forces acting on them. Here’s a selection of roof vents with pitch preferences we have available. Discover more via our wide range of ventilation, including specific sizes: Hambleside Danelaw’s range of tile and slate vents provide ventilation into the roof void, and can also be used with mechanical extraction in bathrooms or kitchens or used for soil ventilation. All of these functions are achieved by the use of an additional flexi-pipe adapter kit which connects the required service to the vent terminal, thereby removing unsightly penetrations through the roof.

If you are suffering from condensation in your loft it will be a “cold roof”. This is the most common type of roof with a loft or attic. A warm roof will have the insulation in between the rafters directly under the roof tiles which means that the loft space will be heated also. They tend to only be used in smaller lofts where the cost of heating a large void space will not be too expensive. The vast majority of lofts or attics in this the United Kingdom are cold roofs, and this is where condensation will occur. It is not likely to occur in warm roofs and if it does there will be other steps to take. How to Ventilate a Loft or Attic to Prevent Condensation How you figure this out will depend on the age and type of property. You can do roof vent size calculation yourself or consult with a professional roofing expert. If you decide to work out the vent amount yourself, consider adding a little extra to the overall total. Don’t go over the top though, as this is difficult to alter in future.Ventilation ridge placed on roof with slit cut into felt to allow warm air out. Images courtesy of roofing ventilation.co.uk A rule of thumb is that, for a normal double pitched roof (IE sloping on both sides) of 15 degrees slope or over, you would need (to vent it properly) a continuous 10mm opening all along the ridge. This would give you a “free” air flow per m, of 1m (=1,000mm) multiplied by 10mm = 10,000mm2. After installation, the condensation levels should be monitored and if found to persist, then it is recommended that an additional row of ventilation panels be fitted between the next lowest roofing underlay overlap on both sides of the roof.