Home Blog Ensure your mid-rift is not too wide!

Ensure your mid-rift is not too wide!


Whilst the width of your girth is probably far more concerning to you than the width of your external door mid-rails, it is possible since the new window energy ratings (WER’s) came in on 1st October 2010 that your door mid-rails might be too wide if adjacent to side panels with matching width mid-rails. These ratings state that any replacement windows (or new build new windows) must have a maximum U-Value of no more than 1.6 W/m2K or be able to achieve a Window Energy Rating of A, B or C.

Before replacing external doors with flag windows or full height vision side panels, it is worth ensuring that the replacement design of the double glazed windows will achieve the minimum energy rating required under the England and Wales Building Regulations, namely a C rating. Most UPVC framed windows with UPVC mid-rifts or dummy transoms will still be able to achieve this minimum energy efficiency requirement, as will most composite door side panels, as these usually have PVCu frames too. The Building Regs don’t apply if there is an inner porch door, or if their is a thermal barrier between the external doors and windows and the house (i.e. between a conservatory and the main part of the home).

However, when it comes to thermally broken aluminium window frames things get a little more complicated, as the greater the amount of metal in any window, the harder it is for a window to achieve the minimum energy rating. Simply put, the thinner the aluminium profile (i.e. frame and sash thicknesses), the more likely it is to have a better rating, and the thicker the aluminium profile, the harder it is to meet the minimum energy efficiency levels required.

Whilst it is OK to have a deep mid-rift (mid-rail) on an aluminium front door, it may not be the case for any attached external window if the window is the only thermal barrier between the outside and the house. Certain upvc and aluminium window products can only achieve a C rating with standard transom sections, so if these are widened it can prevent the window being able to achieve the minimum energy efficiency standards required by the Building Regulations.

So, before replacing side panels to kitchen doors, back doors, front doors or to French door side panels, make sure that any new mid-rift is not too wide!


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Credit is subject to status and affordability. Terms and conditions apply. Finance on windows & doors is available to a maximum loan value of £50,000 with zero deposit. Finance on conservatories is available to a maximum loan value of £30,000 with a 15% deposit. £1,000 minimum order value applies to all finance options. Authorised and regulated by the Financial Conduct Authority. Hazlemere Window Company Limited at Cressex Business Park, Wellington Road, High Wycombe, Buckinghamshire HP12 3PR (Financial Services Registered No. 796507) is a credit broker and is authorised and regulated by the Financial Conduct Authority. Credit provided by Hitachi Personal Finance, a trading style of Hitachi Capital (UK) PLC, authorised and regulated by the Financial Conduct Authority (Registered No. 704348). 12/2019