Conservatory or Extension: Which Adds More Value?

How valuers treat the two

A surveyor measuring a house for a mortgage valuation works to gross internal area, and a conservatory is normally excluded or heavily discounted because it is not classed as year round habitable space. A properly built extension with insulated walls, a solid roof and its own heating is counted in full, which is why it moves the figure and a conservatory rarely does.

In practice a well planned single storey rear or side extension on a Peterborough family home tends to return somewhere around 5 to 10 percent on value, and more if it turns a cramped three bedroom layout into an open kitchen diner. A conservatory more often returns little or nothing, and a tired 1990s uPVC one with a polycarbonate roof can actively put buyers off because they price in the cost of removing it.

Realistic costs in and around Peterborough

Figures move with specification and access, but as a rough guide for this area:

• Conservatory, 3m x 3.5m, uPVC with a modern insulated glass roof: roughly £16,000 to £30,000
• Orangery style room with a solid or hybrid roof and brick piers: roughly £30,000 to £55,000
• Single storey extension: broadly £2,200 to £2,900 per square metre, so a 4m x 4m room typically lands between £40,000 and £60,000 before kitchen fit out
• Add on for structural steel where you remove a rear wall, plus drainage diversions if a manhole or sewer runs through the footprint

Local factors that change the answer

Street ceiling price matters more than most people expect. On a mid terrace in Millfield or Eastfield you can spend £55,000 on an extension and hit the point where no buyer will pay more, whatever the space. On a detached house in Longthorpe, Werrington or Orton Longueville there is usually far more headroom, so the extension makes financial sense as well as practical sense.

Ground conditions vary widely. North and east of the city, towards Thorney and the fen edge, soft or peaty ground can mean deeper foundations or a piled raft, which adds several thousand pounds. On the clay to the west, nearby trees push foundation depths down too. A conservatory on a lighter base sidesteps some of this, which is part of why it is cheaper.

In the conservation areas and stone villages, Barnack, Castor, Elton and Wansford among them, planning officers care about materials and roof form. Matching limestone or reclaimed brick and using a slate roof costs more but is usually the difference between an approval and a refusal.

Planning and building regulations, briefly

Many single storey rear extensions fall under permitted development: up to 4m deep on a detached house and 3m on a semi or terrace, or 8m and 6m respectively under the prior approval process, which still needs an application to Peterborough City Council. Height, eaves and side extension widths are all capped, and permitted development rights are often removed on newer estates by planning condition, so always check your deeds and the original approval.

Conservatories under 30 square metres at ground level are usually exempt from building regulations, provided they are separated from the house by external quality doors and have independent heating controls. That exemption is exactly why they are not counted as living space. Knock the doors through into an open plan layout and the exemption disappears, and the room then has to meet insulation and structural standards anyway.

A simple way to decide

If your reason is resale value, or you need a bigger kitchen, a utility, a ground floor shower room or a genuine home office, build the extension. If your reason is enjoying the garden from spring to autumn on a modest budget, and you accept it as a lifestyle purchase rather than an investment, a conservatory or orangery is a perfectly sensible choice. The middle path many people take is a solid roof garden room with proper insulation, which reads as real space to a buyer at a lower cost than a full extension.