Building regulations - overheating risk in new homes: research report

Research into overheating risk in new homes. Produced in support of proposed improvements to energy standards for new buildings within Scottish building regulations in 2021.

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2. Dynamic Thermal Modelling

Building Typologies

2.1 The building typologies were selected from those used in the overheating modelling work carried out previously in England and Wales. They include a range of typologies and they were shown from the previous work to demonstrate a range of overheating risk. These typologies are detailed in Table 1:

Table 1: Dwelling typologies used to assess overheating risk for Scotland
Type Dwelling Form Size Aspects Ventilation Strategy Heating System Construction Type
1. Apartment / Flat 2b4p Single Nat. vent Individual Mid-rise
1b. Apartment / Flat 2b4p Single MEV (plus nat. vent) Individual Mid-rise
2. Apartment / Flat 2b4p Dual Nat. vent Individual Mid-rise
2b. Apartment / Flat 2b4p Dual MEV (plus nat. vent) Individual Mid-rise
3. Semi-detached house 3b5p Triple Nat. vent Individual Timber frame

Modelling Approach and Overheating Assessment Criteria

2.2 The overheating risk for each of the building typologies was determined through dynamic thermal modelling. The modelling followed the CIBSE TM59 methodology and the results were assessed against the CIBSE TM59 overheating criteria. This is the same approach as used for both the England and Wales assessments.

2.3 Core modelling assumptions (e.g. internal gains, occupancy schedules and window openings) have been adopted from the England and Wales assessments. Details can be found in Annex A.

Building Specification

2.4 As agreed with the Scottish Government team, all buildings have been modelled using a timber-frame build up on the basis that this is the dominant construction type in Scotland. The use of this construction type results in a 'low' thermal mass for the constructions.

2.5 The fabric specification applied to the buildings is based on the '2021 advanced case' in Section 4.5 of the AECOM report "Improvements to Energy Standards for New Buildings within Scottish Building Regulations 2021: Modelling Report – Domestic" (May 2020). These have been summarised in Table 2:

Table 2: 2021 Advanced Case Fabric Specifications
Building Element U-value and details (W/m²K)
External Walls 0.13
Corridor Wall 0.13
Party Wall 0.00
Floor 0.10
Roof 0.09
Window / Rooflight 0.80 (with g-value of 0.57)
Door 1.00

Weather Data

2.6 The TM59 standard requires the simulation to use the DSY1 2020s high emissions scenario, 50th percentile weather data published by CIBSE. CIBSE has published DSY1 weather data for 14 UK locations of which two are in Scotland; Glasgow and Edinburgh.

DSY1 (Design Summer Year 1) is intended to represent a moderately warm summer.

The 2020s weather data is intended to represent 2011 to 2040.

A high greenhouse gas emissions scenario was adopted.

The percentile represents that likelihood that the mean air temperature will be less than predicted (50th percentile used here).

2.7 The TM59 standard suggests that further analysis may be undertaken to account for heat waves and/or future climate change. CIBSE publishes additional weather files to facilitate this including: different future time periods to the end of the century, different Design Summer Years to represent alternative heat wave scenarios, different emission scenarios (low, medium and high) and different percentiles (10th, 50th, 90th percentiles).

2.8 A sample dwelling simulation was run using both the Edinburgh DSY1 2020s high emissions scenario 50th percentile weather file (Edinburgh_DSY1_2020High50) and the equivalent Glasgow weather file (Glasgow_DSY1_2020High50) to determine which resulted in higher overheating risk based on the CIBSE TM59 criteria.

2.9 The results of the sample test showed that the Glasgow weather file resulted in higher overheating results for the sample dwelling. Therefore, the Glasgow weather file was used for the full assessment as it is more challenging to comply with.



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