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

Product Information

I just bought a load of 200mm insulation to top up the loft to see if that would help with the problem. I cleared everything out yesterday and when I went to start rolling it out today I have noticed that the roof is covered in beads of condensation and some of the wood is damp. I'm assuming from the sub zero temperatures last night as there wasnt any rain. We have a full description of the different types of roofs and their insulation in this project, however simply a “cold roof” is one where the insulation in on the loft floor keeps, or is supposed to keep, the warmth in the room below. So, for example, if your roof is 8m long, you would need 8m (=8,000mm) multiplied by 10mm =80,000mm2. We are quite used to seeing condensation in the bathroom, firstly in the form of hot steam as we shower or bathe, but then, as the bathroom cools, the steam condenses on the ceiling, cold water pipes, tiles etc. It is not so obvious in the loft.

In fact, another solution is tile vents. These can be fitted lower down a roof and combined with lap, dry ridge, ridge tile vents and roof tile vents fitted higher up the roof surface to improve air circulation.Usually fitted retrospectively to properties with additional loft insulation recently installed, however the Felt Lap Vent will help to combat the problem of condensation build up in any roof space with a lapped felt/membrane construction. Despite featuring extractor fans in kitchens and particularly bathrooms which create the most moisture that disposes of some of this moisture outside, inevitably some will get through the ceiling or rise through the loft hatch if it does not have a good seal and get into the loft.

Typically a leak will usually have an evident external cause and be localised whereas condensation will be across the whole roof space.

Inexpensive, retrofitable DIY installation

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. 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. There is a calculation that is use to work out the airflow required but it is based on a given airflow requirement. This is determined by building control or another expert, and typically not available if you are trying to find a solution to the ventilation problem retrospectively. 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.

Step two: Work out the number of vents required, asking how many vents it would take to provide the same amount of airflow:

How to Spot Signs of Condensation and Damp in the Loft?

It can be hard to tell if it’s condensation or the roof is leaking, particularly as it can be astounding how much moisture can condense in the right (or should we say, wrong) conditions. Quite often people see some signs of damp in their loft, or water dripping from the underside of the felt or rafters and automatically assume they have a leak. This is most definitely, not always the case.

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. 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. It is recommended that one ventilator panel is fitted between each rafter in the lowest underlay lap above the level of the insulation layer in the loft on both sides of the roof (see product brochure fig. 1). There is no stopping moisture in the home. We create it from cooking, boiling the kettle, washing and even breathing out. This moisture is warm and will rise with the warm air in our houses, eventually finding its way into the loft.Slate roof vent tiles are also ideal for easy installation and the range of designs available. They can blend in nicely with slate tiles. So, if you would like something that suits the slate-style roof, consider these. In very extreme conditions, such as experienced during the ‘Beast from the East’ in 2018, extremely low temperatures combined with fine dry powdery show can create a situation where small amounts may enter through the ventilator. It is not possible to produce a ventilator cost effectively that will allow the free flow of ventilating air and not the very fine snowflakes. Our roof ventilation range is entirely British manufactured, as are the majority of our products; proudly supporting British manufacturing and minimising risk in the supply chain and in your project schedules. Roof and eaves ventilation – complete solutions One issue that can arise is “ice damming”. Many homeowners and professionals who are familiar with these lofts issues know of this problem.