Timloc 5560 Felt Lap Vent (10 Pack)
Features & Benefits
> Discrete profile design
> Easy installation
> 2 spring clips to secure each unit in place
Technical Information
> 3000mm additional free vent area per unit
> Suitable for rafter spacings from 400-600mm centres
> Designed only to enhance existing ventilation via felt/membrane lap joints
> Consideration must be given to increased risk of wind uplift and driving rain resistance outlined in BS5534:2014
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
Please note these are designed as a remedial solution to roof ventilation and do not meet the standards for permanent roof space ventilation on their own and felt lap vents may adversely affect wind uplift of slates and tiles. For more information, please see our blog on the changes to BS 5534:2014 or see BS 5250 Code of Practice for Control of Condensation in Buildings.
