Introduction

You’ve been there: client wants a new kitchen hood or dryer vent, you’ve got one wall, one chance, and zero tolerance for dust, drift, or damp. This guide walks you through the complete process of core‑drilling and fitting through‑wall vents in UK homes—planning, tooling, drilling technique, sleeves and grilles, sealing, and handover. Why this matters? Clean cores with correct fall and airtight sealing keep airflow up and callbacks down. How? A practical, step‑by‑step approach with field‑tested tips, realistic timings, and compliance notes you can use today.

Table of Contents

• Key Takeaways
• Plan the Penetration
• Choose Tools, Bits, and Dust Control
• Drill Clean Cores Through Cavity and Solid Walls
• Install Sleeves, Ducts, and Grilles
• Seal, Firestop, and Document
• Frequently Asked Questions
• Conclusion

Key Takeaways

• Many contractors find that using an M‑class vac with a coring cowl cuts airborne dust by over half and speeds clean‑up.
• In general, a 110–127 mm core suits most 100 mm ducts; go 152 mm for 150 mm cooker hoods to avoid performance loss.
• Set a 3–5 degree fall to the outside (about 5–10 mm per 200 mm) to drain condensate and rainwater.
• It’s common for an unanchored pilot to drift 5–10 mm—use a jig and a firm pilot to keep the hole true.

Plan the Penetration

The Problem

Miss a service, hit a lintel, or choose the wrong core size and you’re re‑patching finishes or throttling airflow. That’s wasted time and a shaky handover.

The Solution

1. Survey and compliance:

   • Check kitchen hood or appliance manual for duct size and maximum run length. Many modern hoods specify 150 mm; reducing to 100 mm often harms performance.
   • Reference Approved Document F (ventilation). Ensure equivalent area and duct size are appropriate for the appliance and space.
   • Consider Approved Document B where penetrations affect fire separation; maintain or restore fire resistance where needed.
   • Planning notes: External grilles are generally permitted development, but listed buildings/conservation areas or leasehold flats may need consent.

2. Service detection:

   • Visual clues: sockets, CH pipes, boilers, meter boxes. Scan if in doubt. A cable/pipe detector and a quick lift of floorboards near the route can prevent grief.
   • Avoid lintels: Keep at least 150 mm clear of window/door heads and check for catnic outlines in the brickwork.

3. Set‑out and size:

   • Common core diameters: 110–127 mm for 100 mm ducts; 152 mm for 150 mm ducts. In general, choosing a core 10–20 mm larger than the duct aids fit and insulation.
   • Mark internal centreline at appliance spigot height. Plot the 3–5 degree fall to the exterior.

Real-World Example

Kitchen retrofit in a 1930s cavity brick wall. Hood spec: 150 mm rigid duct. Set the exit point 350 mm below the ceiling, 500 mm off a reveal to miss the lintel. Core size 152 mm with 5 degree fall. Result: smooth airflow, noticeably quieter operation, no condensation drips.

Choose Tools, Bits, and Dust Control

The Problem

Coring without the right kit leads to burnt bits, dust clouds, and wrist‑jarring stalls.

The Solution

• Core drill with clutch and low‑speed torque. A mechanical clutch is non‑negotiable—contractors often report wrist injuries when drills bind without one.
• Diamond core bits: 110–152 mm set, plus a matched pilot and guide plate. Keep crowns sharp and segment tips clean.
• SDS+ drill and long pilot bit for starter holes and fixings.
• Rig or jig: A suction guide plate or a plywood template screwed at the centre keeps the first bite true. It’s common for cores to wander by 5–10 mm if you start freehand.
• Dust control: M‑class vacuum with a coring cowl or shroud. Many contractors find this cuts airborne dust by over half and reduces clean‑up time significantly.
• PPE: Eye protection, hearing protection (coring often exceeds 85 dB), gloves, FFP2/3 or half‑mask respirator, and non‑conductive boots.
• Water spray bottle for light dampening if needed (avoid over‑wetting occupied interiors).

Real-World Example

On a plaster‑on‑brick wall, a plywood guide with a 152 mm hole, two screws into studs/block, and an M‑class vac connected to the cowl kept the pilot dead centre and the room clean enough that no sheet‑covering was needed beyond a small dust sheet.

Drill Clean Cores Through Cavity and Solid Walls

The Problem

Blown plaster, spalled brick faces, and a chipped cavity closer turn a small vent into a re‑plaster job.

The Solution

Technique: Keep It True and Tidy

1. Pilot first:

   • Drill a 6–8 mm pilot through the plaster and into the masonry at your marked angle. Confirm you’re clear of services.
   • For cavity walls, stop short of the outer leaf; you’ll finish from outside to prevent blow‑out.

2. Start the core slowly:

   • Seat the crown at 200–300 rpm with firm pressure until a groove forms. Then maintain steady load. Don’t "peck"—that’s when crowns snag.

3. Manage the cavity:

   • When you breach the inner leaf, withdraw and vacuum debris. For insulated cavities, insert a short sleeve of thin card or a plastic cone to deflect crumb away from the insulation.

4. Finish from outside:

   • Transfer the pilot to the exterior. Use the core from the outside face to meet the inner cut. This avoids spalling the brick face.

5. Time expectations:

   • In general, a 110–127 mm dry core through standard brick/block takes roughly 10–20 minutes depending on density, bit condition, and operator technique.

Avoiding Common Errors

• Don’t over‑speed the drill; diamond segments glaze and progress stalls.
• Keep the fall consistent. A 3–5 degree fall equals roughly 5–10 mm drop per 200 mm wall thickness—mark it on a small angle gauge if that helps.
• If you hit a flint or hard aggregate, slow down and let the segments work; forcing it risks a bind.

Real-World Example

Solid 9‑inch brick, mid‑terrace. Internal start with a 127 mm core, external finish to protect the decorative brickwork. Total drill time about 18 minutes. Zero face spall thanks to the outside finish and a taped‑on dust catcher box.

Install Sleeves, Ducts, and Grilles

The Problem

A rough hole with a floppy sleeve bleeds air and lets water track back. Undersized ducting throttles performance.

The Solution

Sizing and Components

• Match the duct: If the appliance calls for 150 mm, don’t choke it to 100 mm. Contractors often report noticeable flow loss (commonly around a third) when reducing 150 mm to 100 mm on hoods.
• Use rigid duct or a lined rigid sleeve wherever possible; flex is for short alignment only.
• Fit a backdraught damper and external louvred or cowl grille. In exposed locations, a hooded grille helps with driving rain.

Weathering and Airtightness

• Sleeve install:
  • Cut a rigid sleeve to wall length plus 5–10 mm, maintaining the fall to the outside.
  • Low‑expansion foam or mineral wool to pack the annulus; finish with high‑quality exterior‑grade sealant outside and an airtight seal inside.
• Cavity respect:
  • Keep a slight break in insulation around the sleeve and re‑seal with appropriate insulation tape or foam to minimise cold bridging, while not compressing existing insulation excessively.

Fixing Grilles and Connection

• External grille: Plug and screw with stainless fixings; bed on exterior sealant and tool the perimeter.
• Internal connection: Push‑fit to appliance spigot with a short rigid stub, then clamp. Keep bends smooth and minimal.

Quick Reference Table

Real-World Example

A 125 mm condenser dryer vent in a coastal semi. Used a 127 mm core, rigid sleeve with 5 degree fall, stainless hooded grille, and a quick‑release internal connector for maintenance. Client later reported zero lint staining on the exterior after three months.

Seal, Firestop, and Document

The Problem

Unsealed penetrations leak heat and sound, invite damp, and can compromise fire separation. Poor documentation creates disputes later.

The Solution

• Sealing and fire:
  • Interior: Airtight mastic or acrylic around the sleeve; trim ring if specified.
  • Exterior: UV‑stable sealant and proper pointing to the brick face.
  • Fire considerations: Where the wall is a fire‑resisting element, use appropriate fire‑rated collars, sleeves, or intumescent sealants to restore the rating.
• Condensation control:
  • Ensure the fall to outside, insulate cold metal sleeves through insulated cavities, and avoid long cold runs.
• Commissioning and proof:
  • Quick flow check: Hand over hood on boost; feel for strong discharge and backdraft damper operation.
  • Photo the fall, sleeve, internal and external seals.
  • Note materials, core size, and any fire‑stopping used on the invoice or work report.

Real-World Example

Party‑wall utility room in a converted flat. 100 mm fan through a compartment line: used a fire‑rated duct sleeve and intumescent acrylic both sides. Management company signed off without queries thanks to clear photos and the product datasheets attached.

Frequently Asked Questions

Should I Dry Core Or Use Water?

Dry coring keeps interiors tidy and works well with a good vac and cowl. Light misting can help cool the segments on hard brick, but avoid heavy water use indoors. Wet coring halves bit wear in some cases, but clean‑up can double. Many contractors stick to dry coring for occupied homes and switch to wet only on very dense materials and external‑only work.

How Do I Avoid Hitting Cables Or Pipes?

Read the room: sockets and switches mean vertical/horizontal cable zones; boilers and rads mean pipe runs. Use a detector, check both sides of the wall, and favour clear zones away from reveals and lintels. If in doubt, open a small inspection hole or lift a nearby board to trace routes.

What Fall Should I Use, And Does It Matter?

Aim for 3–5 degrees fall to the outside—roughly 5–10 mm drop per 200 mm wall thickness. It matters: this sheds condensate and rainwater so you don’t get drips inside or damp at the sleeve.

Can I Reduce A 150 Mm Hood To 100 Mm?

You can, but you shouldn’t unless the run is extremely short and the manufacturer allows it. Contractors often report a significant drop in extraction (commonly around a third) and more noise when necking down. Use 150 mm duct and a 152 mm core for modern high‑flow hoods.

What About Cavity Insulation?

Minimise disturbance, keep the sleeve tight, and re‑seal any breaks with suitable insulation or low‑expansion foam. Don’t leave gaps that create cold bridges or let moist air into the cavity. Always finish with airtight seals inside and weather‑tight outside.

Conclusion

Core‑drilled vents are straightforward when you plan the route, size the core to the appliance, control dust, and finish with airtight, weather‑tight seals and the right fall. Do that, and you’ll see faster sign‑offs, stronger airflow, and fewer callbacks.

Want to capture everything on site and send a clean, signable scope the same day? Use Donizo to speak your measurements and photos into a ready‑to‑send proposal, get a legally binding e‑signature, and convert accepted work to an invoice in one click. It saves hours of admin so you can get back to the tools.