Since the time we were developing our new garden space, in which we opened up the area immediately to the west of the house that was previously occupied by the old metal shed and the polycarbonate greenhouse, we'd also been thinking about putting a new window in the home office.
This building was previously an attached garage, but was converted to living space by the last occupiers. Now, just less than half of this former garage space is the office and the remainder is my workshop with the machine tools etc.
I had a vision of sitting at my desk and working while looking out onto our new garden and the open views beyond, over the fields of the adjacent farm. Well, today that vision became a reality...
To start with, I'd bought a complete 1,200 x 1,200 mm (nominal) uPVC double-glazed window unit in an eBay auction for the princely sum of £67. This came off the gable end of a relatively new-built house when the owners were constructing an extension, so it's a modern unit and contains quite efficient glazing panels.
I then spent several days in preparing layouts and calculations in determining the best way of constructing and installing a lintel over the large aperture to be created.
By measuring both the internal and external room dimensions, we established that the wall in question was around 145 mm thick in total. I reckoned this was around 100 mm in the single-course brickwork and the rest in insulation, battens and plasterboard finishes etc. I marked the wall externally with chalk to get a better feel for the size and final installation position. However, this initial mark-out was quickly washed away in a heavy rainstorm !
|the new window and the initial marking out....|
I eventually came up with a combined lintel / side frame assembly to reinforce the single-brick wall both vertically and laterally. Several 3-D CAD models were generated and finite-element calculations carried out before finalising the design.
The lintel as designed is a 1,500 mm length of 120x80x6 rectangular hollow section (RHS), with both ends sealed, and the frame suspended below is from 60x30x5 rolled steel angle (RSA). The 1,500 lintel length gives 150 mm of bearing support at each end of the 1,200 mm opening. The design was arranged so that the outer face of the installed uPVC window frame would be positioned 10 mm behind the brickwork, to allow for filling with silicone sealant.
Afterwards, I sent the construction drawings off to an acquaintance of mine who runs a small fabrication and toolmaking shop, and he manufactured the welded frame assembly and also supplied a loose 2 metre length of 75x75x6 RSA, all for the price of £200 and ready in just a week.
I gave the new lintel frame a base coat of spray primer. The lintel front face is visible after installation, although the rest of the frame is hidden within the construction, but the whole assembly was given basic protection against corrosion.
Installation - Day 1 (evening)
The first job was to drill 12 holes in the 75mm RSA and then mount it to the wall, using 10 mm plastic plugs and steel screws set directly into each individual brick in the course above the new lintel. This would support the roof during the time the aperture was created and before the new lintel / frame was installed. This was a critical part of the project - the window opening was created directly below the apex of the roof, it's made from heavy concrete pantiles, and my (very conservative) estimate was that the new lintel could be supporting as much as 2 tonnes (2,000 kg) of dead load above.
|roof support angle in position and wall marked for cutting|
The conventional way of supporting the wall would be using 'Acrow' posts, in which steel plates are first placed in a couple of slots cut into the wall and then braced from ground level by the posts, which can be adjusted via their screw threads to brace the wall. However, there are a couple of problems with this method; (1) I don't have any Acrow posts (although they are available at hire shops) and (2) the presence of the posts can severely restrict access around the working and installation area.
Installation - Day 2
The idea behind the installation methodology was to minimise disturbance and mess inside the building, so from the outside I cut the vertical window edges in the bricks with my 9" angle grinder fitted with a diamond wheel. I could cut to a depth of around 65 mm with the machine, so the rest of the brickwork would be simply chiselled away. The idea was that the structural elements, i.e. the bricks, would be removed without initially breaking through the interior skin of the wall.
The vertical cuts were made in the wall and I also cut around a brick near the centre of the opening.
|vertical cuts completed - one of the garden|
benches made a convenient working platform....
It was then just a case of patiently drilling and chiselling the mortar until I could remove that first brick, and continuing methodically until the whole opening was made - this took several hours. I cut away the exposed insulation material and stuffed what I could back into the space around the frame sides between the plasterboard and brickwork.
|Opening completed and the lintel frame ready to be lifted....|
The lintel frame was then lifted into position, centralised and some steel packing was added below the end extensions of the RHS to support the beam at its bearing points and to create suitable mortar gaps above and below.
After further level and position checks, the side angles of the frame were drilled and four hammer fixings inserted to initially locate and secure it.
The lintel beam was preloaded by making up small shim packs of steel and aluminium strips I had lying around, and then driving them into the space above the lintel. The first such pack was inserted in the middle of the beam, and I could see the RHS deflect slightly under the load. The centre of each brick in the course was packed out in this way. Then, using part of a bag of ready-mix, the lintel was mortared all around, with a trowel and my gloved fingers to push the mortar as far as possible into the gaps. I didn't apply any mortar to the sides, these gaps will be filled later with expanding foam.
|frame fixed and mortar placed all around the lintel beam....|
Installation - Day 3
Just as well I set up that tarpaulin yesterday evening, because it absolutely pissed down here last night.
However, I was up early and the rain had stopped so I removed the tarpaulin, added a few extra frame fixings and then drilled through the plasterboard at the four corners of the frame. I then cut the board and battens away with a hacksaw blade. I marked and cut from the inside, to minimise the amount of dust generated within the building.
|almost cut right around....|
|first view through the opening created....|
The window frame was then lifted into place and secured with frame fixings at six positions, three down each side. After a general clean up, the gaps around the frame, and between the frame and window, were filled with an expanding foam to reduce the amount of silicone sealant required later. I hate working with expanding foam, it's very messy and gets everywhere...
|from the inside before internal finishing...|
Once the window was fixed, I removed the supporting angle above the lintel and gave the exposed beam face a coat of brick-red epoxy paint. I'll give it a second coat in a day or two.
|from the outside - just needs silicone sealant to make it weathertight....|
Generally, I'm very pleased with the way this all went together. It's been installed for less than a day and already I can't really remember what it looked like beforehand ! It seems such an natural addition to the house now we've extended the gardens.
I've already bought some timber pieces to make up an internal cill and surround, but that's a job for the next few days - let's hope the weather stays fine so I can get outside, finish the silcone sealing and cut the timber for the inside frame.
I'll post an update in a few days when hopefully it will be completely finished.