The Importance of Thermal Bridging

    A typical dwelling built to 2006 standards loses more than 30% of its heat through junctions and around window openings by a process called ‘thermal bridging’.

   For the first time in 2013, UK Building Regulations began to measure heat loss through junctions, this is measured by Y-values (also known as ‘psi’ values). The Y-value in each SAP assessment has a big effect on build materials and cost. If you don’t understand Y-values in your build, you may be paying unnecessary costs.

Thermographic Image Showing Heat Losses Through The External Walls

It is important to familiarise ourselves with terms such as:

• The definition of a thermal bridge
• Types of thermal bridges (repeating, non-repeating and geometrical)
• Psi (ψ) values
• Methods of calculation (1-D, 2-D and 3-D)
• Sequencing of construction processes and examples of common occurrences of thermal bridging.

 

Thermographic Image Showing Heat Loss From Balconies

 

    Thermal bridging can have a significant impact on the thermal and energy performance of the building envelope. In the past, when dwellings were relatively poorly insulated, thermal bridging had little influence on the overall thermal performance of the building. However, as dwellings have become better insulated, the relative importance of thermal bridging has increased. In very well insulated dwellings, the proportional effect that thermal bridging can have on the thermal performance of a dwelling can be significant.

 

Thermal Bridging Calculations For a Steel Structure

 

 

   For example, in a notional semi-detached dwelling (89m² floor area) with a total fabric heat loss of just over 90W/K and a y value of 0.08 (roughly equivalent to a 2006 Part L1A compliant dwelling), then thermal bridging is likely to account for 16% of the dwellings total fabric conduction heat loss (see figure below). If no additional measures are taken to improve thermal bridging beyond this level (i.e. y value remains at 0.08) but the total fabric heat loss reduces by 25% by 2010 and 44% by 2013, then thermal bridging could account for almost 30% of the dwellings total fabric conduction heat loss by 2013.

 

 

   Even when measures are taken to reduce thermal bridging, in very well insulated dwellings, thermal bridging can still account for a significant proportion of the overall fabric conduction heat loss (see figure below).

 

     

 

I   n addition to an increase in fabric conduction heat loss, thermal bridging can also result in:
• An increase in solar heat gains during the summer
• Reduction in internal surface temperatures
• Cold spots occurring within the building
• An increased risk of both surface and interstitial condensation, which may result in mould growth and pattern staining
• Reduction in indoor air quality (due to condensation and mould growth)
• Damage to building components

A   lthough the aim, particularly in low and zero carbon dwellings, should be to try and design and construct dwellings that are thermal bridge free, it is important to realise that it is not generally possible to eliminate thermal bridging altogether. Instead, efforts should be made to minimise thermal bridging as much as is possible.

 

Sources:

http://www.leedsbeckett.ac.uk/teaching/vsite/low_carbon_housing/thermal_bridging/introduction/index.htm

 

 http://www.schock-blog.com/wp-content/uploads/2014/03/thermal-Performance-steel-structure.jpg

 

CPDs and Sustainable Retrofit

   Undergraduate studies and postgraduate studies are never enough if a professional wants to be up-to-date with the market they are involved into.

 

   For architects, engineers and builders, CPD seminars or a regular basis are a must, as they help us catch up with the latest news in the industry, master in innovation and understand how the things that we design work.

 

   As I am personally keen on green design and improving energy performance of buildings, I do frequently look up and read, read, read endlessly about new building solutions, materials, science innovations and so on.

 

   What is best about this is that I can share things I find interesting with you lot, hence the purpose of the Eco-Review BlogSpot (and its facebook page extension...)

 

   In the link at the end of this post, there is an online CPD video seminar to watch, which gives a good insight on Cellular Glass Insulation and how this is applied to all the main parts of a building.

 

   Insulation materials vary so much and it often becomes confusing as per what is suitable where and for what reason.

   For instance, not all insulation materials have a low carbon footprint - in fact usually these tend to provide a lower performance that the oil-based or the mineral ones, but whatever the case, we need to know that the materials we use will perform as we expect them to, as long as they are used where they are supposed to.

   We also need to look at their physical properties, such as their vapour permeability, their compressive strength, the way these are installed, their cost, ease of handling, health implications in the manufacturing process, during installation and post-installation. Physics may be overwhelming for some designers, but it is an essential part to look at, as materials' science is directly related to buildings and therefore, if something is out of our field of knowledge, we should always seek for advice from a specialist and bring them on board in the design process.

 

Source:

http://www.ribacpd.com/foamglas/05864/cellular-glass-insulating-the-whole-building/287539/movie