The Complete Guide to Insulation Fixings: Types, Uses, and Installation Best Practice
Everything you need to know about insulation fixings. Covers the main types, which boards they suit, how to choose the right length, and how to install them correctly on UK masonry walls.
What Are Insulation Fixings?
Insulation fixings are mechanical fasteners used to hold insulation boards firmly against a wall or substrate. They are sometimes called insulation anchors, EWI fixings, or board fixings.
They are used in both residential and commercial construction. The most common application in the UK is external wall insulation, where boards of EPS, PIR, or mineral wool are secured to brick, block, or concrete walls.
Insulation fixings work alongside adhesive. The adhesive holds the board in position initially. The mechanical fixings provide long-term security. They resist wind uplift, prevent the board from sagging or moving over time, and protect the thermal performance of the system.
The fixing must pass through the full depth of the insulation board and embed into the structural wall behind it. The embedment depth into the substrate is critical. It determines how much pull-out force the fixing can resist.
At JALFT, we stock TIMCO plastic and metal insulation fixings in lengths from 50mm to 300mm. All are 8.0mm in diameter and suitable for use with masonry and concrete substrates.
TIMCO plastic and metal insulation fixings in lengths from 50mm to 300mm. Discs, stress plates, and cover caps available. Next-day delivery when you order by 2pm.
Types of Insulation Fixings
There are several different insulation fixing types. The right choice depends on the insulation board material, the wall substrate, and the load requirements of the project.
Plastic vs Metal Insulation Fixings
Both types anchor insulation boards to masonry and concrete. The key differences are load capacity, thermal performance, and the type of pin used.
| Feature | Plastic Insulation Fixing | Metal Insulation Fixing |
|---|---|---|
| Material | Plastic plug and pin | Carbon steel pin with zinc finish |
| Pull-out strength | Suitable for low to medium load applications | Higher pull-out strength for heavier boards and exposed sites |
| Thermal bridging | Lower thermal conductivity. Reduces heat loss through fixing points. | Metal conducts heat. Can cause minor thermal bridging at fixing locations. |
| Corrosion resistance | Plastic does not rust. Suitable for damp environments. | Zinc coating provides corrosion protection. |
| Typical use | EPS and PIR boards on standard masonry walls. Energy-efficient retrofit projects. | Mineral wool boards, multi-storey buildings, high wind exposure zones. |
| Lengths available at JALFT | 50mm, 70mm, 90mm, 110mm, 130mm | 60mm, 90mm, 110mm, 140mm, 170mm, 200mm, 250mm, 300mm |
| Pack sizes at JALFT | 100 pieces per pack | 100 pieces (up to 140mm) or 50 pieces (170mm and above) |
Use plastic fixings where minimising thermal bridging is the priority. Use metal fixings where maximum pull-out strength or a long board thickness is the requirement. On many EWI systems, adhesive and mechanical fixings are used together for the best overall result.
Insulation Discs and Stress Plates
A disc or stress plate sits on the face of the insulation board. The fixing passes through the centre of the disc and into the wall. The disc spreads the clamping load over a wider area of the board surface.
Without a disc, the fixing head can pull through softer or compressible insulation materials when load is applied. This is especially common with mineral wool boards and lower-density EPS.
Always check whether discs are needed for your insulation board type. Mineral wool and lower-density EPS boards generally require a disc or stress plate to prevent pull-through. Heavier boards and windier locations typically need more fixing points per square metre and wider disc coverage. Follow the board manufacturer's guidance or your EWI system specification.
Choosing the Right Length
The fixing length must be enough to pass through the full depth of the insulation board and embed into the substrate behind it. Getting the length wrong is one of the most common installation errors.
A fixing that is too short will not reach the substrate. A fixing that is too long costs more and may not add meaningful holding power. The key measurement is the minimum embedment depth into the masonry or concrete wall behind the board.
| Board Thickness | Recommended Fixing Length | Notes |
|---|---|---|
| Up to 50mm | 50mm plastic or 60mm metal | Shallow boards on internal or cavity insulation upgrades |
| 60mm to 70mm | 90mm plastic or metal | Standard EPS and PIR boards on solid masonry walls |
| 80mm to 100mm | 110mm or 130mm | Common board thickness for UK Part L compliance |
| 110mm to 120mm | 140mm metal | Thicker EWI systems on solid brick or dense concrete |
| 140mm to 160mm | 170mm or 200mm metal | Deep insulation retrofit projects |
| 200mm and above | 250mm or 300mm metal | Passive house or very high performance EWI systems |
These lengths are a guide only. Always check the TIMCO technical data sheet for your specific fixing. Minimum embedment depth varies by substrate type. Concrete and dense brick give better pull-out values than lightweight block or older, softer masonry. If in doubt, carry out a pull-out test on site before committing to a fixing specification.
JALFT stocks TIMCO plastic insulation fixings in 50mm, 70mm, 90mm, 110mm, and 130mm. Metal insulation fixings are available in 60mm, 90mm, 110mm, 140mm, 170mm, 200mm, 250mm, and 300mm. All are 8.0mm in diameter.
Use the filters on the JALFT insulation fixings page to find the right length for your board thickness. Plastic and metal options are available across the most common UK board depths.
Which Boards Need Which Fixings?
Different insulation board types have different fixing requirements. The board material affects how the fixing sits in the board, how the load is transferred, and whether a disc is needed.
EPS (Expanded Polystyrene)
EPS is the most widely used board type in UK external wall insulation systems. It is relatively lightweight and easy to cut. Plastic insulation fixings are generally suitable for standard EPS boards on masonry substrates. The plastic pin and plug keep thermal bridging low. Use insulation discs with lower-density EPS where the fixing head may compress into the board surface under load.
PIR (Polyisocyanurate) and Phenolic Foam
PIR boards offer higher thermal performance per millimetre than EPS or mineral wool. They are used where space for insulation is limited. PIR boards are rigid and dense. Plastic insulation fixings work well with PIR on masonry and concrete substrates. The rigidity of the board means the fixing head sits cleanly without compressing the face.
Mineral Wool
Mineral wool boards are used in external wall insulation systems where the fire strategy requires A1 or A2 rated materials. Mineral wool is compressible. The fixing head can pull through the face of the board if used without a disc or stress plate. Metal pin fixings with a minimum 35mm embedment into the substrate are often specified for mineral wool installations. Always use insulation discs with mineral wool to distribute the clamping load.
| Board Type | Fixing Type | Disc Required? | Notes |
|---|---|---|---|
| EPS (standard) | Plastic or metal | Recommended for low-density EPS | Plastic fixings reduce thermal bridging |
| EPS (graphite, high density) | Plastic or metal | Check with system specification | Greater board rigidity reduces pull-through risk |
| PIR / Phenolic foam | Plastic or metal | Usually not required | Rigid board. Fixing head sits cleanly. |
| Mineral wool | Metal pin recommended | Yes. Always use discs. | Compressible material. Disc prevents pull-through. |
| XPS (extruded polystyrene) | Plastic or metal | Check with board manufacturer | Often used below DPC or in floor systems |
Insulation Fixings and Thermal Bridging
Every fixing that passes through an insulation layer creates a potential path for heat to escape. This is called thermal bridging or cold bridging. The fixing conducts heat through the insulation at each point, which slightly reduces the overall thermal performance of the system.
This matters because UK Building Regulations Part L sets U-value targets for external walls. Thermal bridging through fixings can affect whether the wall meets those targets.
The thermal effect of each individual fixing point is measured as a chi-value (point thermal transmittance). A lower chi-value means less heat loss through each fixing point. Plastic fixings have a much lower chi-value than metal fixings. Where thermal performance is critical, plastic fixings are the better choice.
For EPS systems on standard masonry walls, plastic insulation fixings with their low chi-value keep the overall U-value as close as possible to the board's rated thermal resistance. Metal fixings have a higher thermal conductivity and can introduce a measurable bridging effect at each fixing point, particularly on dense fixing patterns.
On a high-performance EWI project, specify plastic fixings for EPS and PIR boards where reducing thermal bridging is a design requirement. Use metal fixings where the load demands it, and calculate their cumulative effect on the overall wall U-value as part of the building services or thermal calculation process.
How Many Fixings Per Square Metre?
The number of fixings per square metre is not fixed. It depends on the building height, the wind exposure zone, the insulation board type, and the substrate condition.
As a general guide, most UK EWI projects use between 5 and 8 fixings per square metre. Corner zones and edge areas of a building typically need more fixings than field areas, because wind loads are higher at exposed edges.
Every EWI system approved under a BBA certificate or European Technical Assessment specifies a tested fixing pattern. Deviating from that pattern, even by adding extra fixings, can affect the system warranty. Always follow the EWI system supplier's fixing specification and consult a qualified installer or structural engineer if you are unsure.
Installation Best Practice
Correct installation makes the difference between a fixing that performs for decades and one that fails early. Follow these steps on every EWI job.
Step 1: Check the substrate
The substrate must be sound and free of loose material, dust, or contamination. Weak, crumbling, or hollow masonry will not give reliable pull-out values. Carry out a pull-out test before choosing your fixing type and quantity.
Step 2: Prepare the insulation board
Apply adhesive to the board and fix it to the wall. Allow the adhesive to reach the required set before drilling through the board for mechanical fixings. Drilling too early risks moving the board out of position.
Step 3: Drill to the correct depth
Use an SDS drill with a depth stop. Most plugs take an 8mm or 10mm bit. Always confirm the bit size against the fixing specification before drilling. Set the depth stop so every hole reaches the same depth and each plug seats consistently. A hole that is too shallow will not allow the plug to seat correctly. A hole that is too deep wastes drilling time and risks damaging the substrate.
Step 4: Insert the plug
Insert the plug through the insulation board and into the drilled hole. If using a disc or stress plate, place it on the board face before inserting the plug so it seats correctly under the fixing head.
Step 5: Drive the pin
Drive or screw the pin through the plug until the fixing head or disc sits flush with the board face. Do not overdrive. A proud disc telegraphs through the render as a visible spot. An overdriven fixing compresses the board and can reduce pull-out resistance by deforming the plug.
Step 6: Fit cover caps (if required)
On metal insulation fixings, fit a plastic cover cap over the fixing head. This protects the metal and gives a clean finish before the basecoat and mesh are applied. Push the cap firmly into place so it sits flush with the board face.
Step 7: Apply basecoat and mesh
Once all fixings are in place and seated correctly, apply the reinforcing mesh and basecoat over the board faces. The fixing discs and cover caps will be embedded within the basecoat layer, becoming part of the finished system.
Never fix through insulation alone. The fixing must pass through the board and embed into the wall substrate behind it. A fixing that only grips the insulation will pull out under wind load. The structural load must be carried by the masonry or concrete, not the board itself.
Common Mistakes to Avoid
Most problems with insulation fixings come from incorrect sizing, poor installation technique, or the wrong choice of fixing for the board or substrate. Here are the mistakes that appear most often on UK projects.
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Choosing a fixing that is too short The fixing must pass through the full depth of the board and embed into the substrate. A fixing that stops short of the masonry provides no meaningful mechanical restraint. Measure the board thickness accurately and add the required embedment depth before ordering.
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Overdriving the fixing Driving the pin or screw too deep compresses the insulation board around the fixing head. This deforms the plug and reduces the pull-out value. The disc or cap should finish flush with, or just below, the board face. No more.
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Using metal fixings on an energy-efficient system without calculating the thermal effect Metal fixings have a higher chi-value than plastic. On a high-performance EWI project, using metal fixings throughout can shift the wall U-value enough to fail Part L. Calculate the cumulative thermal bridging effect before specifying metal on performance-critical projects.
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Fixing into insulation without a disc on compressible boards Mineral wool and low-density EPS boards require a disc or stress plate. Without one, the fixing head can pull through the board face under wind load. Always check the board manufacturer's guidance on disc requirements.
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Not carrying out a pull-out test on site The substrate condition varies from building to building. Older or softer masonry may not give the same pull-out values as dense concrete. Always test on site before finalising the fixing specification, especially on older buildings with unknown masonry quality.
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Using the wrong drill bit size Most insulation fixings require an 8mm or 10mm SDS bit. Check the fixing specification before drilling. The wrong bit size can prevent the plug from seating correctly or cause the plug to rattle in an oversized hole.
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Ignoring the system specification on fixing patterns EWI systems approved under BBA or ETA certification come with a tested fixing pattern. Deviating from this pattern, even with extra fixings, can void the system warranty. Follow the supplier's specification at all times.
Frequently Asked Questions
Related JALFT Guides
Find the Right Insulation Fixing for Your Project
Plastic and metal insulation fixings, discs, stress plates, and cover caps. JALFT stocks the full TIMCO range with next-day delivery when you order by 2pm.
