Home extension builders


Probuilder can construct your home extension according to the supplied plans or we can refer you to an architect & structural engineer if necessary.  We will work efficiently and with respect for your property & will take account  of the effect our actions on your home-life. Having major building works completed on ones property is always a cause for anxiety.  Our team will keep you in the loop throughout the length of the project.


You can rely on Probuilder to deliver your completed home extension in a timely, professional and considerate manner with the highest standards upheld all round. We'll ensure the client has complete satisfaction and confidence from the start, We will stay in contact with the building control officer and ensure that the structure of the house extension meets building regulations. 

When it comes to furnishing your property, the team are on hand to create the perfect interior finish, including fitting a new kitchen, bathroom fitting, flooring installation, lighting and much more. All of our quotes are valid for 4 months and are all building work is covered by 10 years guarantee. 

Thinking of expanding your home


Before you begin looking for a contractor to build your property extension you'll need to submit planning permission application to the local authority usually at a cost of around £206, along with the relevant diagrams / drawings.  Often enough the building project can be completed under "permitted development" as long as your property is not in an area of outstanding natural beauty, a conversation area or if you live in a flat / maisonette. It is a a legal requirement that the local authority is notified about any property extension.

single story extension
single story extension

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Interior refurbishent located in hammers
Interior refurbishent located in hammers

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view of roof lantern on roof of extensio
view of roof lantern on roof of extensio

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single story extension
single story extension

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How to build a house extension

empty foundation trench ready for concre

The first step to adding a new space in your home is to ensure that it is built on solid foundations. Usually the footing depth is 1 meter but we've gone as deep as 2.5 meters if there is large trees nearby or the foundation trench has been excavated into unstable soil. In extreme cases steel piles filled with concrete can be driven into the ground to achieve the solid base the building requires. The trench can be dug by hand and a lot of hard work where access is restricted.

Filling the foundation trench with concrete

The next step is to fill the trench with concrete and leave it to cure for up to 48hrs. The concrete itself should be cast in a single concrete pour and should never be left to partially dry before another layer is added as this will compromise on the overall strength of the finished foundation. It could also allow water to enter between the layers, the repeated cycle of the water freezing and re-freezing will lead to movement in the foundation. The finished surface on the foundation should be pretty much level & flat.

Brick work to the damp proof course

brick work up to damp proof course.JPG

There must be a clearance of at least 150mm between the dpc membrane and the outside ground level. Care is needed as the dpc membrane is usually the same height as the internal floor although this isn't always the case. The dpc membrane should be installed 1 meter vertically up any existing building walls and behind any wall starter kits. The dpc membrane can have bricks laid directly onto it. You should not fill the cavity with concrete unless your planning on using cavity drip trays and cavity weep vents.

The oversight

The floor area of the extension is filled with crushed granite topped of with a thin layer of soft sand leaving enough space below the finished floor surface to fit in the damp proof membrane and a minimum of 100mm of insulation & the reinforced concrete floor. Consideration should be given to the thickness of floor tiles, adhesives and screeds that will be added to the concrete floor. The finished surface should be as level & flat as possible although perfection isn't essential.

Build the walls


The internal and external walls need to be tied together using stainless steel clips called cavity wall ties. The maximum vertical spacing of cavity wall ties is 450mm & the maximum horizontal spacing is 900mm. If concrete blocks are used then they should meet the specification set out in the drawings. Thought should be given to the roof joist height and any steel beams that need to be installed as this can throw you out and you'll end up cutting bricks to fit.

Add any steel beams

The steel beams are placed on the top of the walls using a genie lift or lots of effort. The beams will need to sit on pad stones. Pad stones have a high compressive strength and are pre-stressed. If a small gap remains between the pad stone then the space should be dry packed with almost dry mortar. Once the dry packed mortar has almost cured any supporting acro props should be removed to allow the mortar to set hard with the full weight of the steel upon it.

Add the roof

extension roof without roof lantern fitt

On flat roofing systems the timber roof strcuture  be added to the building, The timber will generally be added to the inside web of the steel and then sit on top of wooden wall plates that are secured to the top of the walls. There are different types of roofing systems that can be used for the finished roof surface such as felt, fiberglass & resin. All have their pros & cons. On apex roof almost all pieces of timber will need to be cut to size.

Add the doors and windows

The windows and doors will be fitted and subject to the roof being completed any temporary walls will be removed and the building will be water tight. A milestone has been reached & the property will begin to feel warmer. The next stage can commence straight away. Ideally the cavity closures should be installed before the windows or door are fitted.

Add wires and auxiliary 

electrical cables ready for installation

The extension will now be electrified. The wiring will be spurred from an existing circuit to power plug sockets and lighting. If a shower, cooker,  electrical heaters, out door lights are to be installed they should be connected to the consumer unit directly. If there is not enough space in the consumer unit an additional will need to be added. 

Insulate the ceiling

The ceiling will be covered with insulated plaster boards and a vapour barrier. Most insulated plasterboards come with a vapour barrier fixed to the back of them but the seams will still need to be protected. The plasterboards are necessary to achieve a smooth matt finish to the finished ceiling surface. 

Plaster the walls & ceilings

Copy of Fresh plastered wall.jpg

The walls and ceilings will now be plastered. Its likely that some areas will need a thicker coat of plaster than others but overall the finish should be smooth and flat. Depending on its thickness the plaster could take up to a week to fully cure. Generally the plaster is applied in two coats at a thickness of 1 - 4 mm, any thicker and an undercoat plaster known as bonding coat will need to be applied first.

Screed the floor

The floor will need to be covered with a latex based screed. A good quality floor screed can be applied to timber, ceramic, plywood & concrete as long as the surface is primed in the correct way. We typically use sbr to seal the floor surface before the screed is applied.

What next! kitchen, bathroom, office?

Now the extensions is a fully completed shell. You can now turn the new space into your dream kitchen or living area. We can even add a bathroom or a create a smart home. If you cannot decide what form the new space will take then we can refer you to our trusted interior designer who've we worked with serval times prior.




Where we work

We provide much of our services inside the M25 but are happy to travel within the area marked in black. If you require further assistance or advice then use the contact us button or the chat feature in the bottom right of this page.

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