K.W. Harrison & SonsA family building firm

Built properly.Family builders in Bedfordshire, Hertfordshire & Buckinghamshire.

Extensions, loft conversions, renovations and new builds — from the smallest job to multi-million-pound projects, with one team and one point of contact from first idea to finished build.

How the app works

From first dig to handover — a KWH new build, start to finish.

✓ Established over 50 years

✓ Beds · Herts · Bucks

✓ Domestic & commercial

✓ One point of contact

✓ Idea to completion

Where we work

Do we cover your area?

Pop in your postcode — we’ll tell you straight away.

Michael Harrison on site at a KWH new build

Our story

The name on the sign is the family running it.

“Our dad, Ken, started this over fifty years ago with one rule: do it right, or don’t do it at all. Nothing about that has changed.”

Ken Harrison — the K in K.W. Harrison & Sons — founded the firm more than fifty years ago. Now retired, he’s passed it to his son Mike — who runs every job as business and site manager, with the family still out on the tools. When you hire us you get the people whose name is on the sign: one point of contact, from your first idea to the finished build. What’s new is how we work — every quote, photo, invoice and stage shared with you live. Old-fashioned standards, modern technology.

— Mike Harrison · Beds · Herts · Bucks

What we do

One firm for the whole job — idea to completion.

Most builders hand you a pile of numbers to call. We’re your single point of contact: planning, architecture, design, the build itself, and every trade under it — so you only ever speak to us.

Architecture, design & planning

We take your idea through drawings, design and planning permission — the whole start of the journey, handled in-house.

New builds

Ground-up homes and commercial builds, project-managed end to end — up to multi-million-pound projects.

Extensions & alterations

Single & double-storey extensions, structural alterations and refurbishments that add real space and value.

Loft conversions

Rooflight, dormer or a full roof rebuild — attic space turned into rooms you'd actually want to sleep in, staircase included.

Demolition & groundworks

Safe demolition, site clearance and groundworks to prepare the ground for whatever comes next.

Mechanical & electrical

Heating, plumbing, electrical and air conditioning — all coordinated by us, no juggling separate trades.

Decoration & finishing

Bricklaying, plastering, landscaping and decorating — the finishing trades that make a build feel like home.

The KWH app · included with every job

Your build, delivered smoothly — start to finish.

This is what sets us apart. The KWH app keeps your whole project on track: live progress as the work happens, all your paperwork in one place, and a direct line to the team — so nothing slips through the cracks and you’re never left wondering where things stand.

📸 Continuous updates — live photos & progress at every stage

📄 Every document in one place — quotes, invoices & certificates

💬 Direct messaging — talk to the team, nothing lost in texts or email

✅ Approve & pay in a tap — quotes and invoices, sorted

Enquire today, and the moment your job starts, it’s all right here. Prefer the browser? Sign in — it works there too.

Download on theApp Store

A quote in the KWH app — itemised costs with VAT and total, ready to accept in a tap

The family

The people whose name is on the sign.

One family, three generations, one team — the same people who quote your job are the ones who build it. Hover to say hello, or tap to meet each of us.

Michael HarrisonOwner & Team Lead
Matthew HarrisonBuilder
Vanessa HarrisonDirector & Office Manager
Kelsey HarrisonMarketing & Communications
Christopher HarrisonSystems Engineer
Kenneth HarrisonFounder · retired

What people say

Rated five stars by the people who matter.

★★★★★

“We had a double extension done and I was dreading the process a bit if I'm honest. Wasn't too bad in the end. The app was actually really useful — I could just check what stage we were at and what I'd paid so far instead of ringing up every time I wondered. No awkward “so how much do I owe you now” conversations either. Would use them again if we ever do the back of the house.”

Sarah M.Double extension · Leighton Buzzard

★★★★★

“Turned up when they said they would, which shouldn't be rare but is. Cleaned up after themselves too, didn't leave the place a state. Getting photo updates during the day was brilliant when I was stuck in meetings and couldn't check in myself.”

David P.New build · Berkhamsted

★★★★★

“You could tell straight away it's a real family firm, not just a name on a van. Work came out modern and tidy, and they were upfront about cost the whole way through — no nasty surprises at the end.”

Hannah K.Refurbishment · Harpenden

Common questions

Questions people ask us before they book.

Straight answers. Where we can’t give you an exact number without seeing the job, we’ll tell you what drives it instead.

Do I need planning permission for a loft conversion?

It depends on your property and what you're planning — some loft conversions fall under permitted development, others need full planning permission, especially in a conservation area or if the house has already been extended. We handle planning and design in-house as part of the job, and we'll tell you exactly what your address needs before any work starts.

What does a single-storey extension cost in Bedfordshire?

There isn't one figure we can give you, and it's the same story across Hertfordshire and Buckinghamshire — cost depends on the size of the extension, ground conditions, the finish you choose and how easy the site is to get to. We don't publish a generic price list because it would be misleading. What we do offer is a free, no-obligation quote once we understand your actual project.

How long does an extension take?

It varies with the size of the job and how long planning or building control approval takes — weather plays a part too. We'll give you a realistic timeline as part of your quote, and once work starts you can follow progress yourself through our app instead of waiting on a phone call.

Do you handle building regulations?

Yes. Building control sign-off is part of the job — as your single point of contact we coordinate it alongside the build rather than leaving you to arrange it separately.

Which areas do you cover?

Bedfordshire, Hertfordshire and Buckinghamshire. Use the postcode checker further up this page to check your address, or just ask us — we take on the right jobs a bit further afield too.

Can I see progress on my job?

Yes. Every customer gets access to our own app, with live photo updates, quotes, invoices and direct messaging tied to your actual job — so you're not left guessing what stage things are at.

Do you offer free quotes?

Yes — every quote is free and no-obligation. Tell us about your project and we'll come back to you.

Ready to build something good?

Tell us about your project — it takes two minutes, and you’ll have your reference and a real person on it before you know it.

Call 07778 978534