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The Regs: How to get a highly glazed extension to comply with Building Regulations

Posted by wilkinsoncc on June 15, 2018 at 11:15 AM Comments comments (0)

The Regs: How to get a highly glazed extension to comply with Building Regulations


If you have ever wondered how an architect got that glass box extension past building control, then Geoff Wilkinson has the answer



There has been a huge trend in demand for extensions that join internal living spaces to the garden by way of large areas of glazing and ever larger opening bi-fold doors. However this sleek and transparent look desired by homeowners can be at odds with Building Regulations Part L, which sets targets for the building envelope’s energy efficiency.

Part L limits the total area of openings or glazed elements, such as windows, roof windows and doors, to a maximum of 25 per cent of the extension’s floor area. A small extension with a set of patio doors and a lantern light can easily use up this 25 per cent allowance.

An extension that exceeds the allowance is generally referred to as an ‘over-glazed extension’, but they can also be known as sun rooms, orangeries or even glass-box extensions.

Architects will find that, where the 25 per cent rule is exceeded, building control will either reject the plans or request further justification for the over-glazing. So how do you get an over-glazed extension to comply?

Well, although the extension is not compliant on an individual element basis, it could still pass L1B regulations using one of the alternative methods set out in the approved document.

The first thing to do is to deduct the total area of any windows or doors that, as a result of the extension works, no longer exist or are no longer exposed. This is because the heat lost through these elements is no longer being lost. In many cases you will find that this is all you need to do, and a quick schedule of openings versus covered openings may be all that you need.

For example: if an extension has a floor area of 30m² and is covering an existing patio door with an area of 4m² then the extension is allowed to have 6m² (25 per cent rule) plus 4m² (existing openings rule) making an allowable area of 10m². Submit that with your Building Regs application and it’s likely to sail through the checking process.

But if this still isn’t enough then the next option is to demonstrate that the proposed extension is no less compliant than if an extension of the same size and shape was built according to the 25 per cent limit. For example, you could increase the thermal resistance (U-value) of the walls, floor, roof, or glazing elements above the default values in order to increase the area of glass.

From experience I can say that in most cases the heat loss though the glazing will dominate, so start there. Given that the default U-values for walls, floors and roof should all be in the range 0.16-0.28W/m2K, there is not much you can do to significantly improve these. However, the notional glazing has a U-value of 1.6-1.8W/m2K and means that high-performance, gas-filled, low-e-coated glass could see the U-value tumble to 0.9 or better, allowing you more than 40 per cent glazing. Take out some covered-up openings and a 50 per cent glazing ratio is easy to achieve.

But if the extension is very highly glazed (more than 50 per cent), you may need to use the Standard Assessment Procedure (SAP). These calculations should be carried out by an accredited SAP assessor, and demonstrate that the calculated carbon dioxide (CO2) emission rate from the dwelling with its proposed extension would be no greater than the dwelling and a notional fully compliant extension of the same size and shape. This method allows you to keep almost 100 per cent glazing by upgrading existing elements and services within the original part of the house instead – for example, by installing a more efficient heating and hot water system, or increasing the insulation within the existing roof space.

The SAP method allows you to keep almost 100 per cent glazing by upgrading existing elements within the original part of the house

The building control officer may well confuse matters by asking for ‘excess glazing calculations’, ‘SAP calculations’, ‘heat loss calculations’ or ‘thermal calculations’, but in truth all four terms mean the same thing. If you are not qualified to carry out these calculations yourself then I would recommend Googling ‘heat loss calculations for over-glazed extensions’ and you will find a number of consultants that can produce them for you.

In many cases it’s only a couple of hours work for them and a budget of £250 can usually cover it – a small price to pay for that award-winning, highly glazed look on your project.

This Article first appeared in Architects Journal https://www.architectsjournal.co.uk/opinion/the-regs-how-to-get-a-highly-glazed-extension-to-comply-with-building-regulations/10022424.article

Dont get your fingers burnt on a kitchen project

Posted by wilkinsoncc on May 29, 2018 at 8:40 AM Comments comments (0)

The Regs: Don’t get your fingers burnt on a kitchen project

Geoff Wilkinson looks at the potential pitfalls of kitchen, utility and bathroom schemes

Work to a kitchen, utility room or bathroom can seem like the simplest of projects an architect can deal with, but they can be a minefield if you aren’t sure when you need Building Regulation approval.

A very simple refresh with new units and fittings does not generally require approval, however moving sanitary fittings such as the sink or toilet or carrying out electrical works as part of a refit may do so.



Source: Agnese Sanvito

Whitehill Farm, Dunstable, by Hampson Williams Architects

If a bathroom or kitchen is to be provided in a room where there wasn’t one before or you are knocking down a wall (loadbearing or not), Building Regulations approval is likely to be required to ensure the room will have adequate ventilation and drainage, and meet requirements in respect of structural stability and electrical and fire safety. If in doubt always check with a building control body – either the local authority or an approved inspector. Here’s a quick guide to some of the pitfalls to look out for:

Part A Apart from the obvious issues of removing a structural wall, if you are changing the use of a room (eg installing a large bath or jacuzzi in a bedroom) this could increase the load on the floor structure and require strengthening the floor.

Part B Making an open-plan space by removing doors or walls between the kitchen and other rooms, particularly to a staircase, will affect means of escape. Additional precautions in other parts of the property may be needed, such as escape windows, interlinked smoke and heat detection, additional fire resistance or even sprinklers.

Part F When inserting or removing an internal wall, care should be taken not to make ventilation worse. Any new kitchen, a toilet with no openable window; a bath/shower room or utility room should be provided with a mechanical extract fan. The type of room will determine how much ventilation is required. Part F says that where a kitchen previously had only a recirculating fan this can be retained/replaced if it is made no worse. However, I would always recommend fitting an extractor to deal with condensation.

• Kitchen: 30l/s if over the hob and 60l/s if placed elsewhere

• Bath/shower: 15l/s with overrun

• Toilet: 6l/s with overrun

• Utility room: 30l/s

Part H Replacing existing fittings on a like-for-like basis is not controlled. However, if the installation of the fittings will extend or make new connections to a drainage stack or an underground drain, the above-ground wastes and drains are controllable.

Part L If you install or replace a window or external door as part of the works, it will need to comply with Part L Heat Loss in all cases. It may also need to comply with Part A Structure if the opening is made wider; Part K Safety Glazing if the glass is at low level; and possibly Part B Fire Spread if the glass is within 1m of the boundary, for example.

Part J This obviously applies if you install a new boiler, but also if you move the boiler to another location or even if you leave the boiler where it is but extend the flue. Also, if hiding a boiler in a cupboard, take care to ensure there is adequate ventilation and access for servicing.

Part M Another area where you may get caught out is simply moving a ground-floor toilet, since most houses constructed after 1999 will have a ground-floor toilet installed, which has been designed to cater for any visiting wheelchair users. During any refitting, this toilet should not be removed and the accessibility of the toilet should not be made any worse, as it would then be inadequate for future wheelchair users.

Part P Electrical work may be non-notifiable unless a new circuit is provided. For example, installing a new built-in cooker or prefabricated modular lighting is non-notifiable unless a new circuit is required. Even so, be wary of affecting:

• structure (depth of chases in walls, notches in floor and roof joists)

• fire safety (fire resistance of penetrations through floors and walls)

• sound (service penetrations on party walls)

• replacing energy-efficient lighting with inefficient lighting

If a new circuit is being installed or it is within a wet zone (eg adjacent to a bath or shower) then it will require approval or self-certification under Part P.

This article originally appeared in the https://www.architectsjournal.co.uk/opinion/the-regs-dont-get-your-fingers-burnt-on-a-kitchen-project/10031324.article#" target="_blank" rel="nofollow">April issue of AJ Specification


Combustible Cladding Policy

Posted by wilkinsoncc on May 21, 2018 at 8:55 AM Comments comments (0)

The Hackitt report was published last week and like many we were shocked at its conclusions, and importantly its lack of them in relation to cladding.

Given the clear case for action on combustible cladding and the ease with which an amendment could be made by issuing a corrigenda amendment to Approved Document B, we cannot understand why Dame Hackitt did not make this move a top priority.


As it stand there are no changes to the guidance in the Approved Documents and designers and contractors could continue to use Desk Top Studies to justify the use of untested cladding systems. This simply cannot be right.


We note that LABC have produced guidance saying they will continue to accept not only method 3 desktop studies but even method 4 studies subject to certain restrictions. This is all the more concerning as Dame Hackitt has suggested that only LABC should continue to approve High Rise buildings effectively banning Approved Inspectors working on them. This despite both Grenfell Tower and Lakanal House being Local Authority projects.


Over the next few weeks we will be making a series of posts reviewing the Hackitt report and setting out what we believe to be a better and more logical solution to the problems with the current system.


However in the meantime whilst we can continue to deal with High Rise Buildings (and in the longer term on buildings between 18m and 10 storeys) WCCL are today announcing the following policy.


1) We will advise clients to adopt the following strategy set out in BS 9991 2015 as though it supersedes the Approved Document - e.g.


• The external surfaces of walls should meet the provisions in Figure 17.

• In a building with a storey 18 m or more above ground level, any cladding material, insulation product, filler material (not including gaskets, sealants and similar), etc., used in the external wall construction should be of limited combustibility.

• Cavity barriers should be provided in accordance with Clause 19.

• External balconies that are enclosed should be constructed and separated from other enclosed balconies with compartmentation and fire-resisting construction in accordance with Annex D.


2) Where clients wish to use combustible construction despite our advice, then the external walls must meet the performance criteria given in BRE Report BR 135 for cladding systems. We will require full scale test data from BS 8414-1 or BS 8414-2 for the exact system to be used. We will not accept any variation from those test results and or desk top studies in any form to justify the use of combustible materials in systems that have not been tested.


We appreciate that this policy may result in losing projects to other BCB who do not take this approach and that this approach may be challenged by those producing combustible cladding products. However, pending the full outcome of the Grenfell Inquiry and revised updated guidance being issued by MHCLG we do not believe that it is appropriate to do nothing. We therefore call upon all BCB and those involved in construction to adopt the same consistent approach and to provide reassurance to those living and working in high rise buildings that cladding is safe.