Fitting Glass in Oak Frame Buildings: A Capping Guide

Fitting windows and glazed elements into oak framed buildings requires careful planning, as oak is a natural material that will move and shrink over time.

There is often a concern that this movement can place stress on the glazing. This would certainly be the case if glass units were fixed directly into the structural oak frame. As the frame shrinks and settles, it could create gaps around the glazing, allowing air and water to penetrate the building. This can compromise thermal performance, increase heating costs, and potentially lead to damp, mould growth, or damage to the oak frame itself.

There are several ways glazing can be incorporated into an oak framed building. For example, glazing may be fitted into a rebated system formed within an air-dried oak frame, or it may be installed using casement windows set into the oak structure. While both methods can be suitable in certain applications, they can often become problematic down the line.

At Vestra Oak, we have developed our Oak Capping System to counter these problems. This system uses two layers of kiln dried oak boards secured to the external face of the structural oak frame. The glass is then fitted within this capping detail and surrounded by flexible, weatherproof tape to help prevent water ingress while allowing for natural movement in the frame.

This approach allows glazed elements to be incorporated into the building while helping maintain weather resistance, thermal performance, and the long-term integrity of the oak frame.

The capping system comprises of two layers of kiln dried oak boards screwed onto the external face of the structural oak frame which trap the glass onto the frame with weatherproof tape.

Read a short how-to guide below or click here to download the full guide.

Supplied by Us

• Oak Frame and pegs
• Capping Boards PAR to correct size and numbered (these are not cut to length and need cutting on site. 1st stage capping boards can sometimes be in 2 or 3 pieces in length as they are not seen)
• Pre-machined Drip Bead
• 80mm Aluminium Flashing Strips (to be fitted on site and bent into shape)
• EPDM Glazing Tape

Tools Required

• Chop Saw
• Cordless Drill / Screwdriver
• Tin Snips
• Multi Tool / Handsaw
• Orbital Sander – 12.5mm plug cutter / oak plugs
• WD40
• PVA Glue (for plugs)
• Glass Lifters
• Stanley Knife
• Stainless Steel fixings
• Spirit Level
• Tape Measure

1. 1. Once the main frame is complete, start the capping system by screwing the bottom 1st stage horizontals into the main frame, ensuring you use the correct piece according to the numbering on the plans provided. Please note that horizontals typically run the full width of the frame.
2. 2. Next, screw the bottom 2nd stage horizontals into the 1st stage pieces (excluding the drip bead, this is done at a later stage).
3. 3. Then screw the top 1st stage horizontals into the main frame.
4. 4. The 1st stage verticals can then be cut to length and screwed in place. Ensure you leave a 10mm gap at the bottom to allow the aluminium flashing to run the full width.
5. 5. Once the 1st stage is fully installed, fit the aluminium flashing – this is supplied flat, and needs to be hammered into shape to create a 10mm upstand against the oak and 10mm overhang at the front.
6. 6. Then apply EPDM foam tape to the main frame, ensuring it is flush all round the opening edges.
7. 7. Position 19mm packers on the aluminium flashing for the glass to rest on (these can be plastic or cut from scrap timber).
8. 8. Remove the white backing from the tape and carefully lift the glass units into the openings; secure temporarily with screwed timber blocks if needed.
9. 9. Next apply tape to the outer edge of the 2nd stage pieces, cutting away the tape where each vertical member will be.
10. 10. You can now fit the top 2nd stage horizontal to trap the glass tightly against the main frame.
11. 11. Next, install the drip bead. This should be sat on 4mm packers to ensure sufficient gap for water runoff, and check you have enough clearance to screw the piece in without hitting the glass.
12. 12. Fit the remaining 2nd stage verticals – you will need to cut the bottom of each vertical on an angle to meet the drip bead.
13. 13. Plug the screw holes with oak plugs to finish; allow the glue to dry fully before cutting them flush and sanding smooth.

As standard, our glazing system is designed to accommodate a 28mm toughened double glazed unit. Toughened glass provides additional strength and safety, making it well suited to oak framed buildings and large glazed areas.

For projects where improved thermal performance is required, solar control glass can also be specified. This can help achieve a lower U-value, reducing heat loss and improving the overall energy efficiency of the building.

Where required, the system can also be modified to accept triple glazing. This offers enhanced insulation and can be particularly beneficial for projects with higher performance requirements or where maximum thermal efficiency is a priority.

Ready to Discuss Your Oak Frame Glazing?

Whether you are planning a new oak frame project or need guidance on the best glazing approach for your design, our team is here to help.

Book a meeting with our Design Team today to discuss your project and find the right glazing solution for your oak frame.