Thermal bridging happens when heat finds a shortcut through your building’s insulation. Think of it like a hole in a winter coat – even if 90% of the coat is perfectly insulated, that one gap lets the cold straight through.
In building terms, a thermal bridge (sometimes called a cold bridge) is any area where heat passes through the structure at a higher rate than the surrounding insulated sections. This typically occurs at junctions between building elements – where a wall meets a floor, where a window frame sits in a wall, or where a concrete balcony extends through the building envelope.
The materials causing thermal bridges are usually structural ones like concrete, steel or timber that have higher thermal conductivity than the insulation around them. Heat always moves toward cold, and it will take the path of least resistance. A steel lintel above a window, for example, conducts heat roughly 1,500 times faster than an equivalent thickness of insulation.
🌿 Why Thermal Bridging Matters in Ireland
In a well-insulated modern Irish home, thermal bridges can account for 20-30% of total heat loss. That figure is significant. As Ireland’s nZEB building regulations push wall and roof insulation to ever-higher standards, the proportional impact of thermal bridges actually increases. When the insulated sections are performing brilliantly, the weak points at junctions become the dominant source of heat escaping.
Research from Dublin City University found that thermal bridging accounted for 25% of total fabric heat loss in a typical Irish bungalow and 22% in a semi-detached house. These are not fringe numbers – they represent a quarter of all heat leaving through the building fabric.
Ireland’s Building Regulations address thermal bridging through Technical Guidance Document Part L (TGD-L), which governs conservation of fuel and energy in dwellings. The regulations provide Acceptable Construction Details (ACDs) – a set of approved junction designs that, when followed correctly, limit thermal bridging to acceptable levels. The ACDs were updated in 2021 and cover seven construction types including cavity wall, external wall insulation, internal wall insulation and timber frame.
🌿 The Y-Value System
Ireland uses a Y-value (thermal bridging factor) to account for heat loss at junctions in the DEAP energy rating calculation. Two default values apply:
- 🌿 Y = 0.08 W/m²K – where the builder follows the Acceptable Construction Details for all key junctions
- 🌿 Y = 0.15 W/m²K – the default for all other dwellings, whether new, old or retrofitted
The difference between these two values has a real impact on your BER rating. A dwelling using a Y-value of 0.15 instead of 0.08 could see noticeably higher calculated heat loss, pushing down its energy rating and increasing estimated heating costs.
🌿 Types of Thermal Bridge
There are three main categories of thermal bridge, and understanding them helps identify where heat is escaping in any building.
Repeating thermal bridges follow a pattern across an entire surface. Timber studs in a framed wall are a good example – they repeat at regular intervals and each one conducts heat faster than the insulation between them. Wall ties in cavity construction are another. Because they are predictable, repeating thermal bridges are included in U-value calculations for the wall or roof element.
Non-repeating (linear) thermal bridges occur at specific junctions – where a wall meets a floor, where a window sits in an opening, or where a roof meets a wall. These are the junctions covered by the ACDs and are quantified using psi-values (ψ), measured in W/mK. The higher the psi-value, the greater the heat loss along that junction.
Point thermal bridges occur at single spots rather than along a line. A steel bracket fixing a canopy to a wall or a single structural connection are examples. These are generally considered to have a smaller overall impact, though in Passive House design they receive careful attention.
🌿 Common Problem Areas in Irish Homes
Certain junctions cause more trouble than others, particularly in older Irish housing stock and during retrofit projects:
- 🌿 Window and door reveals – where internal wall insulation meets the window frame, uninsulated reveals create a direct heat path. Research shows that insulating reveals is the single most cost-effective way to reduce thermal bridging in internally insulated homes
- 🌿 Wall-to-floor junctions – concrete ground floor slabs meeting external walls are a classic cold bridge, especially in pre-2000 Irish construction
- 🌿 Door thresholds – structural requirements at ground level often create breaks in the insulation layer
- 🌿 Roof-to-wall junctions – where ceiling insulation meets the wall, particularly at eaves level where space is tight
- 🌿 Balcony connections – concrete balconies that extend through the external wall are among the most severe thermal bridges in apartment construction
For homeowners undertaking retrofitting, thermal bridging deserves particular attention. Adding thick insulation to walls while ignoring the junctions can actually make thermal bridging worse in proportional terms – the insulated areas improve dramatically, but the unaddressed junctions remain as cold as before.
🌿 Thermal Bridging and Condensation
Beyond energy loss, thermal bridges create localised cold spots on interior surfaces. When warm, moist indoor air meets these cold surfaces, condensation forms. Over time, this leads to mould growth – a health risk that affects indoor air quality and can trigger respiratory problems.
Ireland’s mild but humid climate makes this particularly relevant. Surface condensation on cold spots near thermal bridges is one of the most common causes of mould in Irish homes. The cold spell before Christmas in recent years has repeatedly demonstrated this pattern – vents blocked, extreme condensation, followed by warmer weather during which mould blooms.
Addressing thermal bridges is therefore not just about energy savings. It is about creating healthier indoor environments, which connects directly to the energy poverty challenge – households that cannot afford adequate heating are often the same ones living with damp and mould caused by poorly detailed building fabric.
🌿 Solutions for Reducing Thermal Bridging
Several approaches can minimise thermal bridging in both new builds and retrofits:
- 🌿 External wall insulation wraps the entire building in a continuous layer, covering most junctions and dramatically reducing thermal bridges – it is generally more effective than internal insulation for this reason
- 🌿 Structural thermal breaks use specialist materials like Compacfoam or Foamglass at critical junctions to interrupt the heat path through structural elements
- 🌿 Insulated foundation systems wrap the entire foundation in EPS, eliminating the wall-to-floor cold bridge that is common in traditional Irish construction
- 🌿 Over-rafter insulation boards (such as wood fibre sarking boards) address the fact that rafters themselves can represent a thermal bridge across 20% of a roof’s area
- 🌿 Aerogel insulation provides high thermal resistance in very thin layers, making it useful for tight spaces like window reveals where standard insulation thicknesses would not fit
For new builds aiming at nZEB or Passive House standard, thermal bridge-free design is a core principle. The Passive House standard requires that every junction achieves a psi-value below 0.01 W/mK – essentially eliminating measurable thermal bridging. While this is ambitious, it demonstrates what good detailing can achieve.
🌿 How Thermal Bridging Affects Your BER and SEAI Grants
The DEAP software used to calculate BER ratings includes thermal bridging as a specific input. A building with well-detailed junctions (Y = 0.08) will achieve a better BER than an identical building with default thermal bridging assumptions (Y = 0.15), all else being equal.
For homeowners applying for SEAI retrofit grants, the BER improvement is a key metric. Addressing thermal bridging as part of a wall insulation project – by insulating reveals, using thermal breaks at thresholds and detailing junctions correctly – can significantly boost the post-retrofit BER, potentially unlocking higher grant tiers.
Builders can also go beyond the default Y-values by having their junction details thermally modelled by an NSAI-approved thermal modeller. If the modelled junctions perform better than the ACD defaults, this improved performance can be entered into DEAP, resulting in a better calculated energy performance. The NSAI operates a certification scheme for thermal modellers specifically for this purpose.
🌿 Frequently Asked Questions
🌿 How can I tell if my home has thermal bridging problems?
Common signs include cold patches on walls (especially in corners or around windows), condensation on interior surfaces, and mould growth in specific locations. A thermal imaging survey can identify thermal bridges clearly – cold spots show up as distinct colour differences on the camera. Many energy assessors and BER assessors offer thermal imaging as an add-on service.
🌿 Is thermal bridging worse in older Irish homes?
Generally yes. Homes built before the 2007 Building Regulations had no formal requirements for junction detailing. Solid wall construction (common in pre-1970s homes) and early cavity wall homes often have significant thermal bridges at every junction. However, even relatively modern homes built to the 2011 regulations can have thermal bridging issues if the ACDs were not followed correctly on site.
🌿 What is the difference between a U-value and a psi-value?
A U-value measures heat loss through a flat building element (a wall, floor or roof) per square metre. A psi-value (ψ) measures heat loss along a linear junction (where two elements meet) per metre of length. Both contribute to total fabric heat loss, but they measure different things. An R-value is the inverse of U-value and measures thermal resistance rather than transmittance.
🌿 Does external wall insulation eliminate thermal bridging?
External insulation dramatically reduces thermal bridging by covering most junctions in a continuous layer, but it does not eliminate all thermal bridges. Junctions at ground level (where insulation meets the foundation), around windows and doors, and at roof connections still require careful detailing. The advantage of external insulation over internal insulation is that it addresses far more junctions by default.