Timber-look styling. Modern thermal performance. Low maintenance.
Flush casement windows sit flat in the frame, so instead of the sash sticking out, everything lines up in one smooth, even line. You get that traditional “timber cottage” look from the street, but with the warmth, security and easy upkeep of modern double glazing.
We supply and fit flush casement windows across Grantham, Stamford, Sleaford, Newark, Bourne, Melton Mowbray and the surrounding areas. Every frame is made to measure for your home.
Sightlines that mimic traditional timber. Optional wood-grain finishes. Period-style handles and stays if you want them. None of the yearly sanding and repainting.
Modern multi-chamber frames, good seals and high-performance glazing help keep rooms warmer in winter and cooler in summer. Lower U-values, lower bills.
Tighter seals and the option of acoustic or laminated glass can reduce road noise, rattles and draughts you get with older timber frames.
Multi-point locking and robust hinges as standard. Toughened or laminated glass available for vulnerable areas.
No flaking paint. No swelling frames. Just a wipe down.
On a normal casement window, the sash (the bit that opens) sits proud of the frame. You see a raised lip.
On a flush casement window, that sash sits level with the outer frame. Everything looks cleaner and more “finished”, especially on front elevations, bay windows and cottages.
It’s a small detail, but it’s what makes the window look more expensive.
In simple terms: same modern performance, better looking from the kerb.
Older timber or first-generation uPVC windows usually leak heat in three places: gaps around the sash, failed rubber seals, and glazing that’s lost its original performance.
Modern flush casement units fix all three:
Multi-chamber frames to slow heat loss
High-performance glazing with low-e coatings
Warm-edge spacers to reduce condensation around the glass edge
Consistent compression on seals, so no “cold corner” in winter
Result: rooms that feel noticeably warmer, especially bedrooms that used to get cold at night and front lounges that caught a draught.
If you’ve got a busy road outside, we can also specify thicker or laminated glass to bring noise down.
We’ll talk you through choices during survey, but here’s what’s typical:
If you’re trying to keep the original look of the house as close as possible, bring photos of how it used to look (even from old estate agent listings). We can work from that.
We know people worry about two things: mess, and being sold to. Here’s how we handle both.
We visit, measure properly, look at your existing frames and talk through finishes, glazing and hardware. It’s a conversation, not a sales pitch.
You’ll get an itemised quote with the style, colour, glass spec, lead time and warranty. No vague “from…” pricing and no surprises later.
Every frame is built for your apertures. This is what keeps the installation neat and the seals tight.
We protect floors, remove old frames and glass, seal up neatly and clean down. Old materials are taken away. You’re not left with a skip.
If you ever need us, you don’t get pushed to a call centre. You speak to the same team who fitted the job.
We visit, measure properly, look at your existing frames and talk through finishes, glazing and hardware. It’s a conversation, not a sales pitch.
You’ll get an itemised quote with the style, colour, glass spec, lead time and warranty. No vague “from…” pricing and no surprises later.
Every frame is built for your apertures. This is what keeps the installation neat and the seals tight.
We protect floors, remove old frames and glass, seal up neatly and clean down. Old materials are taken away. You’re not left with a skip.
If you ever need us, you don’t get pushed to a call centre. You speak to the same team who fitted the job.
Serving Grantham, Stamford, Sleaford, Newark, Bourne, Melton Mowbray and nearby villages.




Not at all. They’re popular on period homes because they look closer to timber, but we’re fitting them on newer builds too. A lot of people just prefer the cleaner, flatter look.
Very likely, yes. Between modern frames, tighter seals and A-rated glazing options, most customers notice less draught and a more even temperature, especially in winter.
In most cases, yes. We can supply a wide range of colours and wood-grain foils, including creams and softer heritage tones, not just bright white.
Yes. You get modern multi-point locking and robust hinges as standard. We can also specify laminated or toughened glass for extra security on ground-floor windows.
Like-for-like replacements usually don’t need planning permission. If you’re in a conservation area or you’re changing the external appearance, we’ll advise before anything is ordered.
A typical three-bed semi can usually be completed in a day or two, depending on access and how many openings we’re changing. You’ll get a realistic timeline with your quote.
Yes. We remove and dispose of old frames, sealed units and packaging. You’re not left with the mess.
Trustindex verifies that the original source of the review is Google. I have been using Avanti for 35 years and the service and product quality is amazing!Posted on Google Will mcintoshTrustindex verifies that the original source of the review is Google. Cannot recommend Avanti enough!! Amazing service from start to finish. The whole team were friendly and professional. Great job and have told all my family and friends if they ever need a job doing, to give them a callPosted on Google Natalie BuxtonTrustindex verifies that the original source of the review is Google. We had nine blown windows, called a couple of window companies to try and get the best price and these guys were the only ones who got back in touch with us. We weren't willing to wait around so went with them and I'm glad we did. They came out, took the measurements and ordered the glass. I was advised the glass could take about four weeks which was fine. Less than a week later I got a call asking if there was any chance they could come later today to fit our new windows! They came round and had them all replaced in about an hour!! For the first time since we've moved into our house we have been able to see properly out of our window! Thank you for the professional and prompt service! I would recommend.Posted on Google Lisa KnightTrustindex verifies that the original source of the review is Google. We have this week had our windows installed courtesy of Avanti Windows Grantham. From start to finish we have had excellent service. I knew I was in safe hands when I met Richard who came out originally to measure up and quote, but to be honest everyone we have dealt with from Richard through to the fitting team have been spot on. Very professional. We did get quotes from other well known window suppliers but the out dated sales tactics and tedious process put us off. There was none of that with Avanti…. It was so easy. I would highly recommend them. I’d give 6 stars if I could👍🙏Posted on Google MARK GOODETrustindex verifies that the original source of the review is Google. Amazing firm and very professional. They’ve done a great job In replacing our conservatory roof for a solid one. Punctual everyday and end result it brilliant. Highly recommendPosted on Google George PimTrustindex verifies that the original source of the review is Google. Avanti delivers an outstanding service. I had a new glass roof fitted on my conservatory and the team also refurbished the whole conservatory and made it look like it was new. Fantastic job, exceeded my expectations. I have no hesitation in strongly recommending this company. A big thank you to the whole team at Avanti, a great bunch of guys!Posted on Google Douglas HowcroftTrustindex verifies that the original source of the review is Google. Brilliant company. Quality windows. Staff really friendly and helpful.Posted on Google Chris JonesTrustindex verifies that the original source of the review is Google. Absolutely over the moon with my windows and doors, service and fitting is top notch!! We will be having replacement windows from them in the future!!Posted on Google Toni BlakeyTrustindex verifies that the original source of the review is Google. A patio door leaked because they "forgot to put in drain holes". Ahe door got fitted by "trimming" the opening by wacking it with a lump hammer (even though the builder was on hand with a diamond saw), the windows came scratched and the external paint could be removed with a finger. I saw they hadn't sealed in the window frames and asked why not. Apparently they don't carry sealant!?!? They all got taken out and my builder rebuilt the door opening.Posted on Google Sheila and PeterTrustindex verifies that the original source of the review is Google. Tony and the team were very professional throughout the whole process. The fitters had to install all new windows and doors and have completed to a high standard. They have been very accommodating with my timescales and would highly recommend. Thank you!Posted on Google Evie English