Most London extension projects go over budget by at least £5,000. Yours doesn’t have to.
67% of London extension projects go over budget. Drawing errors alone cost the average homeowner £4,500 — and that’s before a weak contract hands even more back to the builder.
67% of London extensions go over budget by £5,000+
Drawing errors cost homeowners £4,500 on average
Weak contracts cost a further £6,500
Stop project issues before they happen
We help you make sure your home improvements happen without the drama, nightmares, and stress that are common for major home improvements in London.
Best Practices from Mega-Projects applied to your home
We work closely with you to provide unbiased, professional, and cost-effective advice that injects best practices from billion-dollar projects to your home, reducing your exposure to risk and maximising value for money
About Us
Most London homeowners sign with a builder having never had their drawings independently reviewed or their contract properly checked.
Your architect and builder have no financial incentive to catch their own errors. When problems surface, the cost lands on you.
We review your drawings and contract before a single brick is laid. Our clients typically prevent £8,000–£15,000 in avoidable costs.
“I feel so sick with stress… This is causing so much stress on our relationship.”
London homeowner, on a home extension gone wrong
Ready to make your project a success?
“Cornerstone saved us over £8,000 by identifying a flaw in our architect’s plan — before it became our problem.”
London Homeowner