Part L changes in London came into effect on 1 October 2016

Author Siniat Date 04/11/2016

Part L changes in London came into effect on 1 October 2016
The changes effective from 1 October reflect a Zero Carbon standard for major residential development and a reduction of 35% below Part L for commercial projects as energy use and efficiency remain a particular priority for local authorities in the Capital.

Meeting challenging airtightness requirements
Making the correct choice of sheathing material plays a key role in determining the amount of air leakage in a completed building and thus the amount of carbon emissions.

When the Approved Documents supporting Part L of the Building Regulations came into effect in 2006, a reasonable provision for airtightness was to achieve a pressure test result no worse than 10m3/(h.m2)@50Pa. Today, individual client requirements are regularly specifying some as tight as 1, 2 or 3m3/(h.m2)@50Pa to save on energy consumption and to reduce C02 emissions. See table below for typical standards by sector.

Cement particle board v Weather Defence
Cement particle boards - the traditional sheathing board of choice – are unstable, typically expanding and contracting by 1.5mm per metre in reaction to weather and humidity. This causes air leakage.

In contrast, Siniat has created Weather Defence – a gypsum based sheathing board which is extremely stable. Its dimensional stability is just 0.15mm per metre, ten times less than cement particle board. It has proven to dramatically reduce air leakage on projects, overcoming the most rigorous specifications, even for schools and hospitals which have traditionally struggled to meet the same levels of air permeability targets because of their more complex designs.

This year, for instance - across a number of schools in the Midlands -  the tested permeability of 1.5m3/(h.m2)@50Pa by airtightness consultants HRS Services was significantly better than the 3.0 recommended for schools and colleges. The contractors were able to demonstrate the quality of their installation and avoid delays in handover.

Weather Defence is so effective for airtightness because:
• It is easily manipulated to form tight, clean airtight junctions around complex details
• It is extremely stable, and hardly expands or contracts in reaction to weather and humidity
• As a sheathing layer, it forms an extremely large surface area of envelope and is situated away from internal fittings which might penetrate internal linings.

Normal and best practice standards of air permeability.

 Sector Normal
Best practice
 Dwellings (naturally ventilated) 9
 Dwellings (mechanically ventilated) 5 3
 Factories/warehouses 6 2
 Superstores 5 1
 Schools 9 3
 Hospitals 9 5
 Offices (naturally ventilated) 7 3
 Offices (mixed mode) 5 2.5
 Offices (air conditioned/low energy)  5  2
 Museums and archival stores  1.5  1

Source: BSRIA