3/10/2023 0 Comments Exces glassesWe fully understand that in some circumstances not all construction drawings are complete, we can overcome this in most circumstances so simply contact us for more information (we will send you out a standard from to fill in for missing information). Other scales are acceptable however these are the common ones that are used. Construction drawings can be provided in a hard copy or email format (as long as these can be printed off to A4/A3 to scale), the general scales we work to are 1:50, 1:75, 1:100.INFORMATION REQUIRED TO CARRY OUT EXCESS GLAZING CALCULATIONS * A lesser provision may be appropriate where meeting such a standard would result in a reduction of more than 5% in the internal floor area of the room bounded by the wall.Īs part of the offset in the existing house examples of elements that can be upgraded are if you are having cavity wall insulation installed as part of the works, upgrade the existing roof insulation, new glazing or a new boiler there are other measures if these are not possible. This approach allows substantially more glazing to the extension (if any of the thermal elements to the existing property are upgraded they need to be upgraded to the U-values given in ADL1B as below : Once again a notional calculation is required however in this approach to achieve Building Regulation Compliance the existing property may be upgraded to offset the excess glazing. The first calculation is used in conjunction with the above guidance to achieve a total weighted average U-value for the extension.Ī secondary calculation is used with the amount of excess glazing included and improved U-values to the elements ie walls, floor and roof and glazing (excess glazing may be offset by over insulating just one element or it may be the case that all need to be upgraded.įor this calculation the above information is still required, however in addition the existing property needs to be included. Two calculations are required to achieve Building Regulations Compliance. This approach is suited for extensions that only have a small amount of excess glazing where the U-values of the thermal elements can be improved over and above the guidance U-values. Full SAP calculation (DER Calculations) to include the existing property.The two main methods to satisfy the guidance in part L1B for Excess Glazing Calculations are as follows: Guidance on this can be found in Approved Document L1B. The Building Control Officer will ask for Excess Glazing Calculations, SAP Calculations or Thermal Calculations to justify excess glazing (All three mean the same thing). When Building Control are carrying out plan checking or asking for information under a Building Notice, any extensions which have excess glazing beyond the above guidance will need some form of justification. If the house extension is outside of the guidance in Approved Document L1B, then Excess Glazing Calculations will be required. Glazing area can be in the form of windows, doors and roof lights. Please click our maps for Excess Glazing Calculations in your area.įor an extension not to require excess glazing calculations, it is allowed to have 25% of glazing to floor area and also the area of any existing openings which are being covered or removed as part of the extension work before.įor example, if an extension has a floor area of 20m² and has an existing patio door with an area of 4m² (patio door area being covered by extension) then the extension is allowed to have 5m² (25% rule) plus 4m² (existing openings rule) then the total allowable area would be 9m².
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