The Sealasash Core Service, explained by window type
If your timber windows feel cold, rattly, dusty or noisy, it’s usually not because the glass is “bad” — it’s because air and sound are leaking around the sash through the operating gaps. The Sealasash core service is built to fix that properly, without changing the character of your windows. What we do is common practice in Europe and England, and can be backed up by Historic England.
In plain terms, our core service does three things:
- Gets the window working as it should (so it opens, closes and seats correctly)
- Seals the leakage paths (the fine gaps that let draughts, dust and noise in)
- Keeps it discreet and sympathetic (so it still looks like a traditional timber window)
Below is exactly what that means for each common window or door style, but do note that sometimes custom outcomes have to be completed on-site at the discretion of our carpenters.
Double-hung sash windows & Yorkshire sashes
What’s happening in most sash windows
Double-hungs windows are clever, but they have lots of moving edges: two sashes sliding past beads, meeting rails joining in the middle, and a bottom rail sitting against the sill. Over time, those edges loosen, paint builds up, timber moves, and the gaps become a direct pathway for draughts and rattles. – Honestly, these types of windows had been made with a ‘penny’ gap to allow movement to begin with.
What the core service includes for Double Hung’s
For double-hungs, the core service focuses on the key “bypass” points:
What the core service includes for Double Hung’s
- Side sealing, where the sashes slide
We install discrete brush-type seals into the correct locations so the sash can still move smoothly, but the air gap is dramatically reduced. - Sealing at the parting bead zone
This is the channel the sashes run in. When this area leaks, you feel it as constant cold air movement. - Sealing at the meeting rails
That join in the middle is one of the biggest leak points for both air and noise. We tighten it so the two sashes close together more effectively. - Sealing at the internal beads (staff beads)
This helps stop air movement at the room-side perimeter and reduces sash rattle.
Yorkshire sashes are similar to double hungs but without the parting beads & traditionally operate horizontally.
When you want more noise reduction?
If you’re dealing with traffic, trams, wind exposure or general street noise, we can add extra acoustic-focused sealing at specific rails to further reduce bypass noise. The goal is to stop sound from taking the “easy path” around the glass.
Casement windows, awning windows.
What’s happening in these window types
These styles don’t have the same sliding channels as a double-hung, but they do have a perimeter closing line. If that line is worn, slightly warped, or painted up, you’ll get draughts and rattles — especially in windy weather.
What the core service includes
For these windows, core service sealing is typically a perimeter brush solution:
- Top rail sealing
- Side rail sealing
- Bottom rail sealing
The seals are selected so the window can still close properly, latch cleanly, and feel “firm” when shut.
At times, we may decide that compression seals into new or existing beads is the best approach, and it can depend on the hardware & functionality of the hinged window.
When you want more noise reduction
Where needed, we can use a softer acoustic-style compression seal or double brush with compatible beads to improve contact pressure and reduce vibration/rattle — which is often a big part of perceived noise in older timber joinery.
Timber doors (single or double)
Why doors often feel worse than windows
A door gets constant use, and even small gaps at the sides or underneath can create a noticeable draft. Doors are also a major pathway for dust and noise.
What the core service includes
For doors, we focus on the full perimeter:
- Top and side seals to reduce air and dust infiltration around the jambs
- Bottom-of-door sealing to close off the under-door gap (one of the biggest comfort killers)
When you want more noise reduction
We can upgrade the perimeter sealing approach with double brushes when depth allows, aiming for a tighter, quieter close without making the door difficult to use.
What you’ll feel after the core service
Most clients notice improvements that are immediate and practical:
- Rooms feel less draughty and more stable in temperature
- Windows feel tighter and less rattly
- Less dust ingress and fewer “whistling” drafts on windy days
- Noticeable noise reduction, especially where rattles and air gaps were the main culprits
- Lower energy bills.
And importantly: the window/doors still look traditional— but work the way they should.
Core service vs “new glass”
This is worth saying clearly:
- The core service is about repairing the function and sealing the gaps so the window performs.
- Glass upgrades (laminated, vacuum glass, etc.) can be added, but glass performs best when the window is already properly sealed and seated.
If you’ve ever heard “we upgraded the glass but it still feels cold/noisy”, it’s usually because the leakage paths were never properly addressed. – Read more about this here.
Common problems we’ve found over the years
The bottom line
Sealasash’s core service is the foundation: make it work, seal it properly, keep it discreet. Whether you keep your existing glass or later upgrade it, sealing the operating gaps is the step that makes comfort and performance finally stack up. We are not a cheap fix-it service; we are a quality without compromise outcome. Be careful of ‘retrofit cowboys’ that exist, and our guide to retrofitting for a great outcome can be viewed here.
