Technical Resources & FAQs
Verified technical guidance on historic timber preservation, thermal upgrades, Draftfix draughtproofing, and planning compliance for architects, contractors, and owners.
Architectural Drawings & System Details
Standard junction details, CAD sections, and specification sheets suitable for inclusion in planning submissions and conservation officer packages.
Draftfix Concealed Perimeter Draught Exclusion
Detailed junction drawings showing parted bead, staff bead, meeting rail and bottom rail brush pile carriers.
Heritage Box Sash Cords & Weights Assembly
Traditional horn profiles, pocket access, axle pulley housing, and weight balance configuration.
Repair Care DRY FLEX® Stabilization Detail
Technical application sequence, routing angles, and elastic epoxy integration for decayed cills.
Heritage Glazing Specification Guide
Comparing glazing solutions for historic sash and casement fenestration, from original single glass to vacuum-insulated glazing compatible with narrow period rebates.
| Glazing System | Overall Thickness | Thermal U-Value | Best Suited Context |
|---|---|---|---|
| Historic Single Glazing (Float / Drawn) | 3mm – 4mm | ~5.4 W/m²K | Grade I & Grade II listed properties where maximum fabric retention is required by conservation officers. |
| Slimline / Slimlite Double Glazing | 10mm – 14mm | ~1.9 W/m²K | Conservation areas and Grade II properties where rebates permit slim cavities with narrow sightlines. |
| Vacuum Glazing (Fineo / LandVac) | 8.3mm | 1.1 – 1.2 W/m²K | Heritage sash windows requiring triple-glazing thermal comfort without altering existing profiles or adding excess weight. |
| Standard High-Performance Double Glazing | 20mm – 24mm | ~1.2 W/m²K | New bespoke timber sash and casement installations where traditional proportions meet modern Part L compliance. |
| Acoustic Laminated Heritage Glazing | 6.8mm – 12.8mm | 1.2 – 3.2 W/m²K (Rw 36–40 dB) | High-noise urban corridors, railway-adjacent properties, and commercial heritage developments. |
Frequently Asked Questions
Straightforward answers regarding repair versus replacement, Listed Building rules, the Repair Care system, draught proofing, and commercial contractor delivery.
Restoration & Repairs
How do you decide whether a historic timber window should be repaired or replaced?
Our approach is fabric-first. In most cases, historic timber is slow-grown, dense Baltic pine or pitch pine that possesses greater durability than modern commercial softwoods. We perform a detailed condition assessment: if the core timber framing is sound or can be stabilized using timber splices or the Repair Care DRY FLEX system, restoration is usually both structurally and economically preferable. Full bespoke replacement is reserved for windows where rot has compromised structural integrity or where planning authorities have approved replacement.
What is the Repair Care System and when is it applied?
The Repair Care System (DRY FLEX) is a specialist, flexible polymer resin system designed specifically for timber repairs. Unlike rigid fillers, it expands and contracts at the exact rate of natural wood, preventing moisture ingress and cracked joints. It is used across small, large, and complex moulded profiles on listed and historic properties.
Listed & Planning
Do draught proofing and window repairs require Listed Building Consent?
Like-for-like repairs that preserve existing joinery profiles and timber fabric typically do not require formal consent, although local authorities have varying interpretations. Draught proofing utilizing concealed perimeter brush seals within existing beads is generally favored by conservation officers as a non-intrusive alteration. However, changing glass types (such as retrofitting slim or vacuum double glazing) or replacing complete frames usually requires Listed Building Consent. We regularly provide technical specifications and drawings to support planning applications.
Glazing & Efficiency
What is vacuum glazing and how does it compare to standard double glazing?
Vacuum glazing (such as 8.3mm units) features two panes of glass separated by a microscopic vacuum rather than gas. Because a vacuum contains no molecules to conduct heat, it achieves whole-unit thermal performance equivalent to triple glazing (U-values of 1.2 to 1.1 W/m²K) in a slim profile that fits directly into traditional heritage sash rebates without requiring thicker frame alterations.
How does the Draftfix draughtproofing system work?
The Draftfix system embeds high-density weather pile with a central polypropylene fin directly into replacement timber staff beads, parting beads, meeting rails, and cill rebates. The central fin acts as an impervious barrier against wind pressure and driving rain while the brush pile allows the sashes to glide effortlessly. The system has been independently tested for air tightness and water permeability with over 15 years of proven heritage application.
Working With Us
What experience does Velziyn Projects have on large-scale municipal or social housing contracts?
Velziyn Projects has extensive experience delivering as a specialist contractor on major public and housing association frameworks. Notable projects include the survey and installation of 200 heritage units at Holly Lodge Estate (£350,000) and multi-year window refurbishment across 200+ street properties in Camden (£3.5m) working alongside Keepmoat and TRC Contracts Ltd.
What accreditations and safety qualifications do your operatives hold?
Velziyn Projects is CHAS Accredited, with a Constructionline application currently pending. All site operatives hold verified CSCS qualifications and enhanced DBS certification. Health and safety protocols are managed professionally via BrightHR / BrightSafe, with tailored RAMS (Risk Assessments & Method Statements) produced for every site.
Have a Heritage Window Project?
Whether you have a single window or a large programme of works, our team will provide a professional, detailed response to your enquiry.