Hambleside Danelaw Felt Lap Vent
Hambleside Vents - Danelaw Felt Lap Vent - HD ULV-B
The underlay lap ventilator is designed for simple professional or DIY installation from the inside of cold pitched roofs where condensation is a problem.
It is designed to fit between the overlaps in the roofing underlay below the tiles or slates to introduce ventilation openings where there is no proper provision for roof space ventilation or existing ventilation air paths have been blocked, particularly when the loft insulation has been upgraded.
The shallow and tapered design of the panel suits all commonly encountered rafter spacings and allows for easy fitting between the roofing felt or underlay.
It is retrofitted to reduce condensation in the roof space. Simple for anyone to fit from inside the loft by simply inserting between the overlaps of underlay.
Airflow: 3,200mm2 per vent.
How Many Vents Do I Need?
The number of felt lap vents can be worked out using the following formula:
Selecting the amount of airflow, then dividing the roof length by the spacing (in meters) indicated below.
| Free Flowing Airflow | Felt Lap Spacings | |
| Millimetres | Meters | |
| 5000mm/m ² | 600 | 0.6 |
| 10000mm/m ² | 300 | 0.3 |
| 15000mm/m ² | 120 | 0.12 |
For Example:
For a roof that is 7m requires airflow of 10000mm/m ²
7/0.3 = 23.333 or 24 felt lap vents evenly spaced.
For roof spaces that require more than the 15000mm/m ² the spacings half for each additional 5000mm/m ²
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