A charming Pembrokeshire roof, constructed from raised collar trussed rafters and enhanced with dormer windows. The owner is fortunate to have stunning views over St Dogmaels and along the Teifi estuary. The combination of slate and stained facia board are very easy on the eye.
Designing the Pembrokeshire Roof Trusses
Raised collar roof trusses offer the building designer the option of a vaulted ceiling, through the elevation of the bottom chord or ceiling tie. As with this St Dogmaels project, raised collar trussed rafters can be used to provide extra headroom by pushing the ceiling up into what would otherwise be the loft or roof void.
Raising the bottom chord of the truss in this way reduces its effectiveness as a restraining (tensioned) member. Naturally the truss now generates a increased degree of lateral or horizontal force at the wall-plate and relies on the wall’s ability to resist it. The truss designer is constrained by a limitation placed on the amount of outward movement. This limitation is deemed to be safe and will have been considered by your building designer.
The building designer is also aware that the roof slope below the collar will now be formed solely by the rafter. With limited rafter depth the choice of insulation becomes very important and must be adapted accordingly. There are a number of modern solutions including composite insulating quilts and dense polystyrenes. Adequate ventilation must also be incorporated and sufficient space left between the covering layers