BUILDING A HOUSE EXTENSION

FOUNDATIONS  1. 

The foundations have been excavated and the concrete has been laid and levelled. The required depth will be different for each individual extension as there is no way of having a standard depth. 

The building inspector will insist you dig down until you have found good firm ground. With most houses the ground level is (made up) with back fill, this can be anything from builders rubbish to type one hardcore.

The top soil is the first layer of ground to be excavated normally at least 6 inches, 150mm deep, this can be saved and re-used around the garden to make up ground levels.

The cost of ''muck away'' is not cheap so re-cycling is essential to keep the costs down. Not all extensions are built on the same type of foundation there are other types of ''footings''.

Some are built on a reinforced concrete slab or even piles and ground beams. Whatever the method good foundations are essential

FOUNDATIONS 2.

The first few courses of bricks are also essential. These bricks should be a good quality engineering brick or trench block. The amount of courses laid will depend on the depth of your footings in the ground. Building regulations insist engineering bricks are at least two courses above finished ground level before regular facing bricks or blocks can be used. A damp proof course (DPC) is required at least 6 inches or 150mm above finished ground level.If you are not sure what a facing brick, DPC or engineering brick is? Then you can post your question to me on my blog where I will be happy to give a more detailed explanation.

CAVITY WALL 3. 

Once the damp course has been laid we started to build the cavity wall using thermal blocks on the external and internal walls. The cavity between the two walls was 65mm and both walls were 'tied' together every 3 courses with butterfly cavity wall ties. This would allow room for the cavity wall insulation to be inserted in between the ties.

I also drilled and fixed track wall ties to the original houses external back wall where the new extension walls would meet. Two tracks were drilled and fixed to the house and the ties were hooked into the track every course. This type of brick tie is a wall track tie. There are several types of wall ties on the market. 

WINDOW (REMOVING EXISTING) 4. 

A window was removed from the house and was blocked up using thermal blocks. Screw in wall ties were drilled and fixed into the cavity wall to tie the new block work into the existing brick wall.

I did not lay the blocks to the top of the window opening, The reason for this is the block work would become part of the internal wall of the extension and this would not be seen. The top part of the window opening would be above the roof line and would be visible once the extension was built.

So this section would have to be bricked up using bricks to match existing wall and also matching up with existing bonding. 

WINDOW (BRICKING UP) 5. 

I cleaned up and re- used some of the original bricks that were removed when I knocked down part of the existing wall to create an opening between the extension and the house.

We used screw in ties to tie in brickwork, this created a straight joint. The best procedure to create an invisible repair would be to 'tooth' out the existing brickwork.

This process would involve cutting out any half bricks and mortar on either side of the window opening and laying full bricks. The bricks would also tie in the new brick work. This method would not need the use of any brick ties.

I did not use this method on this extension to save myself time. The brick work would be visible but only if I were standing on the extension roof or looking out of a neighbours window.

The method I used was less time consuming and a cheaper option. Later photos will show how the repair blended in so well it was not noticeable. 

CAVITY WALL (INSULATION) 6. 

The cavity wall insulation was inserted as the wall was being built.I used a thermal wall insulation board 65mm thick. This insulation was perfect for fitting in between the wall ties, which were used every three courses.

When buying insulation for your home, you will find that the government have been subsidising the cost of insulation for the past few years. Most DIY stores have offers like buy one get one free! Or as long as you do not mind signing a disclaimer saying you are buying the insulation for DIY purposes and not for a new build then there are more discounts on offer!

This is to encourage homeowners to reduce there carbon footprint by insulating there homes. 

If your home is well insulated then you won’t be burning as much fuel to heat your home and so producing fewer emissions into the environment.

BLOCK WALL (INTERNAL) 7. 

Building blocks come with many different properties. They are suitable for a variety of applications.

Some of the different properties are fire resistance, sound and thermal insulation. 

CAVITY WALL 8.

The picture here shows the 65mm cavity, brick external wall and the block internal wall. You can see the insulation board and the wall ties.

A cavity enclosure can be purchased to cap the end of the cavity wall. This is attached prior to fitting the door frame. 

BRICK WALL 9. 

The wall piers facing the garden were built using a cheaper alternative brick that would look like the original London stocks. This was the cheapest option, getting the closest match to the existing house brick possible. London stocks can cost between £1 - £1.20 per brick.

Most builder’s merchants will offer quite a wide range of alternatives, although you can still buy stocks new. Reclaimed London stocks are also normally on offer at most merchants. The difference between old and new is purely the old ones have weathered and stained over the years and will blend in better with older buildings. A reclaimed stock has a certain character about them and if the odd one has a bit of paint or soot on it this seems to enhance the wall. 

The only difference between the old stock and the new will be old stocks will be the old imperial measurement.

Where the new stock will be metric.

Unless you specify you want imperial when buying. 

BLOCK WALL (INTERNAL) 10. 

The internal wall height is determined by the height of the existing ceiling of the house. This also applies to the existing floor level. 

The bonding in the brick and block work should line up to guarantee a good bond. The brick courses of the house and the extension should line up and be level.

This photograph gives the impression that the courses are not level but they are! The window opening was blocked up using blocks.

Each block is the depth of three courses of bricks. The block work on the window opening was started one course higher as you can see in the picture but the bond remains the same.

                   

BLOCK WALL (INTERNAL) 11.

This picture shows the internal wall, cavity insulation and external wall.

The walls were built in stages; the reason for this is that when using thermal blocks to build walls I find after four or five courses there is too much movement in the wall.

So the best thing to do is to leave what has been built for a while to 'go off ' (set).

So I moved to another section of wall and built that until I had laid five courses. I then returned to the 'set ' wall and carried on building that. 

BLOCK WALL (BOUNDARY LINE) 12. 

When applying for planning permission from your local authority to build an extension. They will contact your neighbours to see if they have any issues with the proposed work.

On previous extensions I have built, building control have insisted on a cavity between the external walls of neighbouring extensions even if your neighbour did not have an extension this would still apply.

But over the last few years I have noticed that now consent is being given to build right up to the property's boundary line on either side,this does not mean you can build an extension the full length of your garden but you may be granted permission to build to the the full width of your back garden (this would only apply  where the boundary line of the back garden is the same as the boundary line of the property .)

In this picture you can see the new extension was very close to the neighbour’s window.

CAVITY WALL 13. 

This shows the wall cavity. The door frame I am using will but up against the brick and block work covering the cavity and will not need a cavity wall enclosure. 

A wall cavity enclose is a plastic moulding made to fit different size wall cavity's.It is quite common to find door frames fitted without using cavity enclosures. 

BLOCK WALL / BRICK CORNER 14. 

This is how the front extension external wall will tie in with external block side walls. The corners of the extension are built out of brick, so only brick will be visible from the back garden. Unfortunately the neighbours never got the same view! 

BRICK WALL (PIER) 15. 

This picture shows one of the two brick & block piers built on both sides of extension to support the RSJ.

The external brick pier was built using alternative stock bricks,

I bought these for a third of the original the price. These bricks were rejected for being miss-shaped (banana bricks) but this did not compromise there structural strength. 

RSJ (SOLDIER COURSE) 16.

A small piece of DPC was bedded onto the piers. The RSJ was lifted and bedded into position making sure it was perfectly level. DPC was rolled out onto the RSJ before a soldier course of bricks were laid. The same was done on the inside but no soldier course was used with the block work. 

RSJ (BLOCK WORK) 17.

The 65mm cavity between the brick and block work was maintained above the RSJ. Wall ties were used to tie the two walls together and cavity wall insulation fitted. The RSJ was fitted allowing15mm tolerance around door frame. 

BRICK WALL (FACING/BONDING) 18.

All the brick work had to be level, all the joints even and the bonding straight, as this is the 'face' of the extension. (The part everybody See's)The brick courses on the piers had to be perfectly level with each other so when the RSJ was fitted the bonding above the RSJ matched the bonding on the piers. The RSJ was 8mm thick, this meant that it was important to make the joint in the brick work the same as the rest of the wall and no thicker. A wider joint would make it obvious where the RSJ was sitting. It was important the RSJ sat back at least 5mm from the face of the wall so it could be pointed over with mortar. This would hide the RSJ making it invisible on the finished extension.

PROPPING (CEILING & FLOOR) 19. 

The supporting wall between the extension and the kitchen had to be knocked down to create one room.

It was important to have one ceiling height rather than have two ceilings separated by a beam. When this is seen in extensions it means the beam is there because the RSJ was fitted below ceiling height and had to be boxed in. When knocking down a supporting wall it is essential you get a qualified builder to do this, or consult a structural engineer before attempting. The first thing I did was to support the kitchen ceiling. To do this I used scaffolding boards and adjustable steel props. I made sure the floor was strong enough to take the extra load I was going to put on to it, luckily the floor was concrete.

As soon as the supporting wall is removed all the weight  of the upstairs floor and kitchen ceiling would be on the floor supporting the adjustable steel props. If the floor had not been concrete but was floorboards and joists then I would have had to lift the floor boards and prop from the solid ground below the floor cavity.  To support the ceiling and upstairs floor I had to support the joists. To support each one individually would mean using loads of props as the joists were 450mm apart. This would limit my work area and would mean knocking a hole through the ceiling to find every joist.

So instead I used a scaffolding board and placed it along the ceiling and in between the steel supporting props. This way I could use fewer props by spreading the load. There would be no need to locate the joists as I would be able to place my supports any where without risking going through the ceiling. I also used scaffold boards in between the concrete kitchen floor and the support props, this is to stop the risk of the props slipping. 

  PROPPING A LOAD BEARING WALL 20. 

To prop the load bearing wall I used adjustable steel supports, scaffolding boards and attachable wall supports. The wall supports are designed to be knocked into brick work joints without removing any bricks! But I am yet to find a supporting wall that will allow such an easy installation. So first of all I cut out an outside brick from the supporting wall where I wanted to fit a wall support. The inside course of bricks I raked out as much of the joint as I could. The wall supports are a steel plate that you can slide onto the square foot of an adjustable steel prop. Once I had slid the support onto the prop I then adjusted the prop to the height I needed to allow me to hammer the wall support into position. I then placed a cut piece of scaffold board under the support prop, between the prop and the ground. The next step was to tighten the prop so it would take the weight once the wall was removed. Each prop has to be perfectly level and after tightening, the height adjustment pin should be locked into position. This method was also used on the ceiling props. The props should be no more than 600mm apart. This picture shows two wall supports and props. The first prop was fitted at a lower level but when I attempted to fit the second one I found an obstruction so I had to go in at a higher level. I used four props and eventually they were all fitted at the same height. 

PAD STONE 21. 

I marked out the area of the wall I wanted to remove, and cut a line in the wall using an angle grinder with a 125mm diamond cutting blade. I knocked out the brickwork saving as many bricks as I could. Once the wall had been demolished. Building regulations specifications required two load bearing pad stones to be installed.

PAD STONE 22. 

The pad stones are a solid concrete base 3 bricks deep and spanning from the external wall over the wall cavity and onto the internal wall to support each end of the reinforced steel joists.I made two shutters one for each wall and poured some concrete into the shutters Levelled of and tapped the sides to remove any air and left them to cure.

REINFORCED STEEL JOISTS. (RSJ) 23. 

The RSJ arrived as two separate beams and four joining plates that connected the two beams and created the required wall cavity.Once they were assembled I could now lift it and cement into position.

The existing floor and ceiling joists had to be fitted tightly into the new RSJ. Any gaps between the joists and the RSJ are packed out using slate. DPC is laid onto the RSJ prior to installation. This will provided a damp barrier for the existing floor joists to sit on. DPC is also used between the RSJ and pad stones. DPC is laid on top of the RSJ before any brickwork is laid. Eventually all of the RSJ will be covered with DPC to prevent cold spot. 

Once the gap in between the wall and RSJ has been bricked up and left to set the wall supports can be removed and the holes they have left can be bricked up. 

               REINFORCED STEEL JOIST  
                      (65MMCAVITY) 24. 

The 65mm cavity between the RSJ was specified by building regulations. Four steel spacers were bolted in between the two steel joists.The original wall cavity was bricked up to create a solid wall. 

SOIL VENT PIPE.BATHROOM WASTE 25. 

The original soil vent pipe was not moved. I cut a hole into the cast iron pipe and fitted an air tight rubber pipe adaptor sleeve.The upstairs bath and sink waste pipe was re connected to the soil vent pipe. The pipe will eventually be boxed in when I do  the dry lining. 

ROOFING (JOISTS) 26.

The roof joists are cut to length and slotted into the RSJ. Noggins were cut and fitted between joists this will maintain the 450mm centres required. The noggins will also prevent the joists from twisting. Noggins are required for every two meters of non supported span.

ROOFING (JOISTS) 27. 

 All the roof joists and noggins were 150mm x 50mm.

Internal block walls were kept lower than external walls this is because the external wall will create an up stand on the roof and the internal wall will help support roof joists. The up stands will help stop surface water running into neighbour’s property. The extension was built so close to the boundary line there was not any room to allow for gutters to be fitted to the sides. 

RSJ (ROOF JOISTS / DPC) 28.

Before slotting the roof joists into the RSJ a layer of DPC was laid inside for the roof joists to sit on.

ROOFING (MARINE PLY) 29. 

Once all the roof joists were in place and all the noggins were in the next step was to fix firings to the top of the joists. Firings are strips of timber the same width and length of the roof joists, but the depth of the firings start at whatever depth is required to create a fall in the roof to meet building regulations. This will be the depth of one end of the firing and will run down to 0 at the other end. Creating a fall in the roof which makes the surface water run in the direction required. Lay the ply on the roof joists and 

Starting from the edge of the house lay the sheets of Marine ply one by one. There are several types of ply but the only type approved for flat roofing is marine ply normally 18 to 22mm thick. When laying the ply as long as the joists are 450mm apart from centre to centre then you should find the join between sheets will be above a joist allowing both sheets to be fixed down side by side, without having to ad extra noggins.

The joists can be marked out onto the ply to save having to try and locate them once the sheet is down and pushed home. I used a chalk string line to do this.

Nailing down should be150mm apart. Along the edge of the up stands and house a 50mm arris rail was fixed to the edge where the ply met the wall. 

ROOFING (PERFORATED UNDERLAY) 30.

New regulations (nearly been in force for 10 years) covering extra insulation on flat roofs require a perforated under felt to be laid and then an external layer of insulation on top.

The perforated underlay is rolled out across the ply roof and is not glued to the ply sheets but left loose. The perforated underlay is designed to allow the ply roof to breathe. 

ROOFING (PERFORATED UNDERLAY) 31. 

I believe the reason for this new regulation is obviously to reduce carbon emissions but also to prevent the first layer of felt from being glued to the roof ply. This not only makes it difficult to remove but it also means that more often than not the ply deck gets so badly damaged when trying to remove the old felt that this also needs replacing. If the ply is not replaced it will defiantly mean that the surface the new layers of felt are being laid on will be uneven.

Shortening the life expectancy and efficiency of the new weather proof covering. The weather proof covering should be floating on the roof structure to allow the timbers to breathe and expand and shrink according to the change of humidity. If the water proof layer is glued to the roof structure this will cause the water proof covering to crack or split when the roof timbers expand and shrink.

ROOFING, EXTERNAL INSULATION 32. 

The roof insulation I have used here is 100mm thick foam board with a layer of under felt attached. These can come in different sizes and thickness. The boards were laid on top of the perforated underlay, staggering joints and placing any cuts along walls rather than along the edges.

This type of insulation can be cut easily with any type of hand saw

ROOFING (FASCIA BOARD) 33.

A 150mm fascia board was fitted to the end of the roof joists and the roofing felt was laid over the fascia. 

ROOFING (GUTTER DRIPS) 34. 

The gutter drips are made to finish on the top of the first stuck down layer of felt with the inner edge at least 200mm from the edge. 

I made the welted drip by cutting the felt to suitable lengths about 350mm (14 inch) I nailed each length to timber battens along the edge of the roof with the felt underside facing out and with the sheet hanging down. I glued the sheet down to below the timber batten, hanging the gutter and formed a fold back up to the roof line and then folded the remainder back onto the roof. I applied adhesive to the drip (the fold from the nails down and back up) together and returned the sheet to the roof deck applying a 200mm length on top of the underlay. The Top Sheet will overlay the under layer finishing about 25mm from the edge of the roof. 

ROOFING (FELT) 35. 

I applied three layers of glass fibre reinforced roofing felt. Using a cold pour application. This can be painted on to the surface you want to bond giving a generous coating on each layer. The cold application method is slowly becoming more popular amongst professionals although most still use torch on or hot bitumen methods. The first layer of felt is layer from the left side to the right side of the roof starting at the lowest point.

Each layer overlapping the first by 150mm and each overlap receiving a generous coat of cold bitumen adhesive. The second layer running from back to front edge using the same method. The third layer being laid exactly the same as the first. This creates a cross, cross of each layer with the top layer running parallel with the roof edge. All joints overlapping in a down ward direction.

ROOFING (SILVER REFLECTIVE BITUMEN PAINT) 36. 

This is an alternative to the traditional mineral cap sheet. The traditional mineral cap sheet protects the felt from cracking and splitting by trapping moisture in the minerals.

The minerals also protect the black felt from getting to hot in the sunshine. The downside to this method is that the mineral chippings trap dirt and eventually encourages growth. The silver bitumen coating creates a reflective covering that will not get hot in the sunshine but will keep the roof cool in the summer. The reflective coating is also very smooth and will not trap any dirt. Instead it will help any fallen dirt to be washed away in when it rains. I applied two coats of the reflective coating to the whole roof. This can be relocated at any time

to prolong the roofs life expectancy. 

ROOFING (COPPING STONES) 37. 

Coping stones were laid onto the up stands securing the ends of the roofing felt. The join between the house and the roof was covered using a lead flashing. Fitting the flashing involved chasing out a mortar joint into the wall two courses above roof line.

I bent the flashing to create a 15mm lip on a 90% angle. I tucked the 15mm lip into the open joint and sealed it using a grey roof sealant. 

FLOOR CONSTRUCTION (WOOD) 38. 

The floor used for this extension was a wooden floor construction. Using 150mm x 50mm floor joists and 18mm tongue and grooved moisture resistant floor panels. The cavity between the floor joists and ground level had to be a minimum of 150mm.Two vent bricks were built into the brick wall of the extension threshold. These were below floor level. A damp proof membrane was laid on top of the ground and sealed. DPC was laid on to the internal threshold wall. Joists were bolted to the internal extension walls 18mm below existing kitchen floor level. Another joist and DPC was laid on top of the existing wall, which had been reduced to accommodate new floor joists.

FLOOR CONSTRUCTION 39. 

The floor joists were laid 450mm centres apart and were fixed at both ends using standard leg joist hangers. Instead of using noggins I used 450mm herringbone joist struts. These can be bought from most suppliers.

The floor panels were laid at a later date after electrical and plumbing work had been completed. 

RENDERING 40. 

Both side walls were rendered with two coats of sand/cement/waterproof mortar mix. This picture shows the first coat drying. Once rendering was complete a six foot fence was erected either side of the garden.

FITTING OAK BI-FOLD DOORS 41. 

By this stage all structural work was complete. The next step was to install the sliding oak doors and frame into the opening. 

OAK FOLDING PATIO DOORS 42.

Before these doors could be fitted I decided to varnish every door and frame part with 3 coats of external varnish. The fitting instructions said these doors could only be fitted where an RSJ had been installed above the door opening. This was due to the weight of all the doors and frame especially when fully opened. To fit the frame into the opening I first had to assemble it. The instructions insisted the top of the frame had to be drilled and bolted to the RSJ. This meant drilling several holes into the RSJ and it also meant where ever there was a bolt there had to be a nut and washer on the other side! So I cut out a brick for every bolt hole. This was so I could fit the nut and washer and tighten it.

The rest of the frame could be fixed into place using regular frame fixings. I sealed around the frame using expanding foam. A whole day was taken up just installing the frame. 

OAK FOLDING PATIO DOORS 43. 

The next day I started to fit the doors. The first door went in nice and easy.....but then! All the other doors had been labelled to make installation easier so I continued fitting the second door even though I knew something was wrong. I realised the doors and hinges were not going to marry up. Eventually I worked out which door was what and totally disregarded the labels. I don’t know if I had accidentally swapped labels when varnishing or if it was a manufacturer’s error. But a lot of time wasted. 

OAK FOLDING PATIO DOORS 44.

After that the doors went in as easy as clockwork. The adjustable hinges made installation so easy and I was very impressed with the quality of these doors.

OAK FOLDING PATIO DOORS 45.

Within two hours I had all the doors in and gliding on there runner’s quite weightlessly.There was a lot of draught excluder to fit to the doors and each door could be locked independently.

There were pop out handles to help pull these big doors open, but I found they were only needed to pull the hinged edge out when the doors were fully closed. These doors glided like a feather when pulled open and they folded up nicely when open taking up very little space. 

OAK FOLDING PATIO DOORS 46. 

The locks on each door meant that you could have just one door opening on its own or have two, three, four or five. Fitting these doors was like the icing on the cake. The construction of this extension had gone smoothly from day one. I have fitted many bespoke folding patio doors but these were the most impressive so far. Who made them? Well I don’t like to promote a single company when there are so many other good ones out there but I must say I give thumbs up to Wickes for these quality doors.