Compression Tape on New Windows - Should I Insist?

Compression Tape:
When I asked a prospective installer of new (replacement) double-glazed windows about use of compression tape around the sides, he was interested, appeared prepared to consider it and noted that on the written quote - tho he said he hadn’t heard of it before, his firm (Malbern) haven’t been using it. He mentioned the more-standard sealants and expander foam, etc.
It’s presumably worth my while pressing this point… How much of an improvement does compression tape give? Is the clearance between window-frame and aperture substantially different, compared to the sealant etc methods? (Malbern manufacture their own window assemblies.)

Preventing Spillage of Cavity Insulation:
I also raised ‘cavity closers’, to prevent the insulation beads recently installed in the cavity from spilling out… He said they’d ensure that was addressed and wrote it on the quote, however I’m actually quite worried about that, as any spillage could result in cold patches.
Thanks folks,
Mike Killian

Proper taping gives an airtight fit. Foam and trim don’t. If the use foam against your wishes you can rescue the situation with Blowerproof.

I would hope the beads were coated in a slow cure adhesive. Check with the installer if your contract is unclear. If not, and there aren’t cavity closers already in place, you could be up s**t creek without a paddle. It becomes a three man job to remove the old window and you will still loose some of the insulation.
(Keep any insulation that escapes and refill the top of the cavity as the insulation settles to its new level.)

Ok, thanks Tim. I’ll push the windows-installers to use tape, eg Iso-Chemie, or Illbruck products.

The CWI paperwork says, ‘…EPS beads are coated with a bonding adhesive… to bond and set the EPS beads and to make the bead-fill stable…’ - which the installer demonstrated for me at the time. I’ve emailed the main guy who directed the job (from the office) to ask for clarification. I’ll also get back to the windows-quoters, for more detail on how they address CWI.

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…actually had a good chat with the CWI main man, who rang me up to discuss what can be done about the question of retaining your CWI during window-installation, how they could help afterwards if necessary etc, so that’s good. (I didn’t press him on charges, at this point.) And the windows people themselves say, Yes we do use compression tape, mostly on new-builds where walls are still square!, but willing to do so if that’s what we want, etc.

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Remember that you will probably need thicker tape than the installer normally uses to allow for the irregularities of your reveal.

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I would insist on the compression tape being applied as the sealants etc can degrade , shrink and move. Here are some numbers from Vitaseal that should help-
Compression protection values from uncompressed to 75% compressed:
0% no compression - Protects against the ingress of Dirt, Leaves + Insects.
30% compressed - Air flow, Dust + all the above values.
50% compressed - Thermal loss, Acoustic transmission, + all the above values.
75% compressed - Driving rain, + all the above values.


Thanks Lloyd - so, as a test for your 50% level that insulates thermally, I’m basically looking for the tape to be at least 50% compressed, ie less than half the thickness of what a short piece of tape left aside on a nearby table-top would expand to?
On others’ helpful advice, I’m further considering cutting-back mortar/plaster about a cm behind/inside the newly-fitted window-frame, then airtight-taping the frame to the exposed brickwork, then re-instating mortar/plaster to back of frame, ie overlapping the airtight-tape. Good plan…?

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Compressed to 50% the fully expanded height (This should be given in the specification along with the selected width required)

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I am wondering whether compression tape alters over time to a fixed size, dependent on its compression, or whether it remains flexible, changing its form to allow for changes in the gap between window frame and reveal. The latter could be particularly useful for timber structures with change in humidity or materials with highly differing coefficients of expansion.

Anyone know?