Conservatory roof replacement in Bath

The conservatory frame carries the roof's weight down to the base. In most conservatories the frame is made of uPVC or aluminium sections around steel or aluminium reinforcement, with a lightweight roof sitting on top. A solid roof puts more load on those sections, and at a different point, so the structure has to be checked before the design is fixed.

The ring beam is the key part. It is a horizontal beam, in timber, steel or reinforced aluminium, that runs round the top of the frame and ties the posts together. In a solid-roof conversion it receives the foot of every new rafter, so it spreads the roof's weight evenly along the frame instead of leaving it on a few posts. Where there is no ring beam, one is usually added. Where there is one, we confirm that it is sound and large enough for the span.

Checking the base

The weight passes from the beam, down the frame and through the dwarf walls to the foundation. Dwarf walls are the low brick or stone walls that most conservatories stand on, and they can hide problems. Cracks, slipped courses, or a wall built without proper bonding show up when the load increases. A foundation too shallow or too narrow for a tiled roof is a risk worth finding out about before the roof is bought, not after.

The MyBuilder guide lists frame and foundation upgrades among the main cost drivers for a conservatory roof, and our experience agrees: the roof covering is rarely the surprise, the structure underneath sometimes is. We therefore check the frame, ring beam and base first, and report in writing what each one will carry.

When the frame cannot take a tiled roof

If the structure cannot take the weight of a tiled roof, the answer is rarely a hasty rebuild. A lightweight system, with panels or small-format lightweight tiles, can give you a solid, insulated roof at a fraction of the load. In some cases the frame can be reinforced with steel and kept, and in others the conservatory is better rebuilt in part. We show you the options, with what each changes, so the decision is yours.

Whichever route is taken, the structure is checked against the Building Regulations. Approved Document A covers structure, and a covering that adds significantly to the load needs its own check. The body that checks the work, B&NES Building Control or a private approver, will want to see the calculations.

We keep records of what we find at this stage, with photographs of the frame, the beam and the base, so that the file given to building control reflects the conservatory as it actually is.

For the detail of what is checked and why, our guide to structural checks before a solid conservatory roof goes through the frame, beam and base. The answer on whether a tiled conservatory roof is too heavy addresses the question owners raise first.

The reason people give for replacing a conservatory roof is nearly always temperature. A thin transparent roof loses heat quickly in winter and gains it quickly in summer, and nothing indoors can fix that. A solid, insulated roof can.

Insulation in a pitched conservatory roof goes between the rafters or over them, or both. Rigid boards of foam are common because they give a good insulating value in a slim depth. They are cut to fit between the rafters, with a gap left above for ventilation where the design calls for it, and often topped with a second layer across the rafters to cover the timber itself. Timber is a weak point for heat, so covering it matters as much as filling the gaps between.

Air and moisture

A warm room full of moist air is the setting in which condensation forms. A vapour control layer, a sheet laid inside the insulation, facing the room, keeps room moisture from reaching cold timber. Tapes seal each joint. Above the insulation, a breathable membrane lets any moisture that does get in escape while keeping rain out. Where the design includes a ventilated gap, vents at the eaves and ridge keep air moving.

These layers have to be built in the right order. Insulation placed without a vapour control layer, or with gaps around the edges, can trap damp and cause condensation in the timber. We follow the manufacturer's instructions for the system, because the layers are tested together and do not work in isolation.

Thermal standards

A solid roof for an existing conservatory is notifiable work, and the body that checks the work will say what thermal performance it expects. Approved Document L, the part of the Regulations on energy, sets limits for new fabric elements in existing homes, and Table 4.2 gives a figure for the roof of 0.15 W/(m²·K). Whether and how that applies to a conservatory depends on how it is separated from the house, so we do not assume. We ask the building control body and design the build-up to the answer.

Inside, the finish is a plasterboard ceiling or a lined timber soffit, and recessed lights are possible where the design allows. Spotlights and fans go in before the ceiling closes, and it is much easier to plan them in advance.

Our guide to insulating a conservatory roof covers boards, panels and what works with each frame. If condensation is your main complaint, the answer on whether a solid roof stops conservatory condensation explains the cause.

The junction between a conservatory roof and the house wall is a stress point. The two structures move differently, one rigid and heavy, the other light and slightly flexible. Rain runs down the wall and has to be led onto the new roof without getting behind the cladding. In many leaks blamed on the roof, the water is in fact entering at this line.

The standard detail uses lead. A flashing, a strip of metal that bridges a joint, runs up the face of the wall and laps over the roof covering. In older work the top edge is tucked into a groove cut in the masonry, called a chase, and held with wedges and sealed. A soaker is a small folded piece of lead laid under each tile course, with one edge turned against the wall beneath the flashing. Together they stop water running behind the covering.

Stone walls and older houses

In Bath the wall is often limestone, and the lead has to be fixed into it without harming the stone. A chase is cut into the joint, not the face of the block, and pointed afterwards in a mortar that suits the wall. A cement mortar can trap damp and damage soft stone, a point the Bath Preservation Trust has made in its comments on repointing at a Walcot listed building, where it urged lime mortar. We use a lime-based mortar on older stone and leave the choice of detail to the building's character.

If the wall carries a damp-proof course, or if the old roof was fixed at a height that would bridge it, we check where the new junction sits. A flashing that crosses a damp-proof course can let moisture track upwards. We keep the lead above it.

Gutters and drainage

The roof also has to shed water. A conservatory gutter is typically small, and a solid roof sheds more water faster than a glazed one, so we size and fall the gutter to suit. Downpipes are checked to make sure they take the flow. If the roof meets a house gutter or a valley, we deal with that junction too.

Finally, the wall is made good, the plaster or render around the junction is repaired, and the site is cleared and swept. You receive the building control paperwork once the final inspection has been passed, and your written guarantee covers the finished work.

For a conservatory on a protected house, our guide to conservatories on listed and conservation homes explains the consent question. If the wall junction is already leaking and you want a stopgap, the page on conservatory roof repairs covers seals, bars and flashings.