Why Over-Cladding a Conservatory Roof is Dangerous: A Critical Warning for Homeowners

It sounds like the perfect solution: transform your freezing conservatory into a warm room quickly and cheaply by simply wrapping the existing roof in insulation and tiles. It’s often called a “wrap-over” or “clad-over.”

However, what many “cowboy” installers fail to tell you is that this method is often structurally dangerous, thermally flawed, and potentially illegal. At KJM Group, we spend a significant amount of time replacing failed cladding systems that have caused leaks, cracked plaster, and rotting frames.

1. The Physics of Failure: Interstitial Condensation

The biggest enemy of a clad-over roof is invisible. It’s called Interstitial Condensation.

When you bolt insulation over an existing glass or polycarbonate roof, you trap the original roof structure inside the new layers. Warm, moist air from your home rises into the ceiling void. When it hits the cold surface of the old aluminium bars or glass (which is now buried deep inside the roof), it turns into water.

Because the roof is sealed up, this water has nowhere to go. It sits there, soaking into the new timber battens and plasterboard. Over months and years, this causes:

• Dry Rot & Wet Rot in the timber frame.
• Mould Growth on your new ceiling.
• Electrical Failures if water tracks down light fittings.

2. The Structural Weight Risk

Your original conservatory was engineered to hold plastic or glass. It was likely built on shallow foundations and used lightweight PVC window frames as support.

A clad-over system adds significant weight: timber battens, insulation, plywood, tiles, and plasterboard. If the original window frames buckle under this new weight (especially with snow load), the roof can collapse.

3. Visual Proof: The Proper KJM Process

Don’t just take our word for it. Look at the work involved in a compliant installation. A “wrap-over” installer skips all of these vital steps.

🔍 Step 1: New Structure

🔍 Step 2: Insulation

Step 2: High-performance rigid insulation is fitted to meet U-Value targets.

🔍 Step 3: Finish

Step 3: A professional plastered finish with integrated lighting.

🔍 Step 4: Completion

4. Comparison: Cladding vs. Replacement

Is it ever worth the risk? Here is a direct comparison between the “cheap fix” and the “proper solution.”

5. The “Unsellable House” Trap

Even if the roof doesn’t fall down, it can hurt you financially when you try to move.

When you sell a house, the buyer’s solicitor will ask for a Building Control Completion Certificate for any solid roof conservatory. Because clad-over systems rarely meet the U-Value requirements of Part L or the structural requirements of Part A, getting this certificate retrospectively is often impossible.

We frequently receive calls from distressed homeowners asking us to rip off a clad-over roof and install a compliant one just so they can complete their house sale. Don’t pay twice. Do it right the first time.

Frequently Asked Questions