The New Part L and NHBC Conservatory Construction

Good news is contained in the new Building Regulations Approved Documents L1A and L1B that deal with the conservation of fuel and power in new buildings and existing buildings.

L1A and L1B are very similar, with L1B being the more demanding. Anyone constructing a conservatory or porch that is attached to a dwelling must construct it in a manner that complies with the new energy efficiency provisions. October 1st 2010 is the date this comes into force.

Exemption (of the energy efficiency provisions) will only be granted where:

The conservatory or porch is at ground level only.

It has a floor area of less than 30m².

The doors and windows in the wall to which the conservatory is attached are retained, or if removed they are replaced with substitute walls, windows or doors that meet the new energy efficiency requirements.

The heating system of the dwelling must not extend into the conservatory.

If the conservatory fails to meet all four of the above conditions, it is deemed not to be exempt and must comply with the relevant energy efficiency requirements (4.8 and 4.9).

And if it is not exempt, it must be treated as a conventional extension in which case all applicable Building Regulations apply.

Under Building Regulations, the cavity wall below the roof level of the new conservatory must not suffer damp penetration. But with the outside skin above the roofline exposed to rain, dampness readily gravitates downwardly below the roofline and into the conservatory. Just flashing the intersection is not sufficient.

The remedy and compliance is achieved using preformed cavity trays that are inserted into the masonry just above the roof intersection. With versions to suit horizontal and sloping abutting roofs*, all styles of conservatories can be protected from dampness.

‘At last there is an official line to take regarding cavity trays and conservatories’ advised a spokesman of Cavity Trays of Yeovil. ‘As a rule of thumb trays will be necessary, unless the addition is exempt. Conservatories have departed from the original dictionary definition of a glazed housing for plants and are now commonly used as extensions of the living space, so it makes sense to regularise the construction integrity’.

It is interesting to note that the NHBC advocated some years ago that trays should be fitted above conservatory roof intersections. Now its view is reinforced and from October 2010 it is thought over 90% of all conservatory proposals will be non-exempt, and thus will have to be constructed to the new Building Regulation standards.

‘Regulations are guiding this change which should result in conservatory contractors offering the same standard and compliant scope of build where the roofs attach to the original structure’

* Type E cavitrays for horizontal intersections.

* Type X cavitrays for sloping intersections.

Both manufactured by Cavity Trays of Yeovil from which a brochure dealing with the compliant interfacing of conservatories is available upon request.

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