Diy Conservatory Building Roof

Conservatory Roofing
One of the drawbacks of any addition to the home, be it conservatory, sun lounge or whatever, is the further you go out in depth the lower the roof pitch must become. With roof tiles, roof pitch is critical and every manufactured tile has a minimum pitch to which it can be laid and still relied upon to keep the rain out.

Glazed conservatory roofs, however, are not so demanding and low pitches are common on conservatories: given the position of the upstairs windows and the depth of the addition, pitched roofs are of no more than 20 degrees and sometimes even less. Technically speaking, even flat roofs have a pitch to then because a slope angle of less than 10% is described as flat. If the rainwater is going to run off efficiently to the gutters, a good fall is essential and it pays to keep the pitch as steep as you can.

Many conservatory lean-to roofs are technically flat roofs because of this, and there are roofing systems glazed with polycarbonate that have received BBA (British Board of Agreement) approval down to 2.5 degrees. At this slope the water will trickle off to the gutter where the fall is about the same as around the fascia. The improvements in plastic roof technology are testimony to the fact that this can be done, with sealing between the glazing bars and the flashings of the system roof. However a low pitch will advance the ageing process and, with it, all the bad things that can happen to a roof later in life.

The steeper the angle, the faster rainwater runs off and the greater the self-cleaning ability of the glazing, reducing the susceptibility to algae growth and leakage.

Holding down the conservatory roof
Odd as it may seem, solid roofs are not always as well anchored down as glazed ones. A solid roof covered by slates or lightweight tiles can be lifted by the suction or the wind passing over it. To compensate, steel straps are fixed over the wall plate and down the walls. Roofing systems that use polycarbonate sheets have to combat this wind suction differently: here, the sheets are locked down by the glazing bars and their covers, and these bars are screwed down to the rafters and eaves beams. Screws are normally installed at 400 mm – to hold down the roof not to support it.

With holding down straps that usually have to be fixed to the masonry of the inner leaf, the fixing isn’t always easy. Lightweight aerated blocks can’t be nailed into with any conviction and plugging and screwing these straps on is essential if they are to work. The dead weight of the roof is sometimes enough to hold the roof down against wind uplift but for the extra cost it is worth putting straps on anyway.

Plastic conservatory roofing
Acrylic has better light-transmission properties than polycarbonate, (i.e clearer) but it seems to be restricted in the construction industry to shower doors or the windows of public aquariums. This demonstrates how strong and flexible the material can be. Transparent tunnels that let you walk through underwater environments are made of acrylic and can resist great pressure. Acrylic is normally sold for use in greenhouses or secondary double-glazing. Some leading skylight manufacturers have been using acrylic in preference to glass for many years now. One disadvantage is that it scratches quite easily but a positive is that it can be worked on site – sawn, cut and drilled.

Polycarbonate sheeting
Most conservatory roofs are glazed with polycarbonate sheets. In 20mm thickness with a cellular structure made up of 5 walls, this has a considerable resistance against breakage. Manufacturers claim it is 200 times stronger than glass. The cavities are not hermetically sealed in their manufacture the way double-glazed windows are sealed which means they offer less resistance to the passage of heat. It is difficult to find an accurate quote for the “U” value for polycarbonate sheeting in the way that windows and doors are quoted by conservatory companies (impressive “U” readings). Compared to single-glazing the twin walls of polycarbonate sheets are much better insulated but compared to the low-e coated or argon filled double-glazing we use today, the polycarbonate is hopelessly flawed. Security is another issue when opting for a roof like this as it can be sawed through with a junior hack saw.

The good points of polycarbonate are that it is cheaper than glass, quick to install and lightweight. Beware, some cowboy builders do not bother to support it against the house wall but just use self-adhesive tape to weather this abutment instead of lead. Algae can render the material permanently green if rainwater is slow to run off or it is situated near trees. It is only when a 25 mm multi-wall thickness of this material is used that the thermal U value becomes comparable but then you lose extra light. Pretty much all polycarbonate sheets sold as roofing have a Class 1 (BS:476:pt 7) fire spread rating making them suitable for use anywhere in dwellings.

Typical DIY polycarbonate roof
As polycarbonate is so easily available in sheet form you can obtain it and create a simple lean-to with it yourself.

Cutting and preparing the sheets
Calculate the sheet sizes and number of glazing bars needed before you start and prepare the sheets cutting them to size. Generally speaking these are easy to cut – either a sharp knife or fine-tooth saw.

As the hollow pockets aren’t hermetically sealed, you will have to tape the ends up to try and limit the build-up of condensation. Weatherproof and perforated breathable tape should be used which allows trapped vapour to be released. Design your conservatory, if possible, to accommodate standard sheet sizes to avoid cutting and waste.

Cavity trays to facing brick walls
Before the sheets go up and block the access, you need to prepare the flashing and install a cavity wall tray DPC at the abutment between the roof and wall. Trays aren’t necessary on external walls that are clad with rendering, boarding or tile hanging; if these are in good condition they should keep out the rain. Because facing brickwork in cavity walls in only 112 mm wide (single brick) it is porous and prone to being penetrated by wind-driven rain. It didn’t matter when it was the external skin of a cavity wall but now that its part of the brick skin becomes internal to your conservatory, it’s a problem. To prevent rainwater saturating the wall above the roof and draining down into the new addition, a cavity tray needs to be installed. The cavity tray should be installed first and it’s always best to use a proprietary remedial tray that can be installed in pieces as you work across the roof, fixing one sheet at a time. The preformed remedial trays are rigid and stand up in the cavity, leaning against the inner leaf to drain water forwards; if they are to work well and keep your conservatory below them dry, they need to overlap and have an upstand at the free end to prevent water cascading off inside the cavity. They also need to have weep-holes for drainage in the perp joints of the occasional brick and little plastic fillers can be bought to fit these. Positioning of the trays is important.

Flashings
This element is the cover over the joint of roof and wall. Obviously it can’t be dressed down until the roof is on but the brickwork can be cut to allow for it. Flashings come in a variety of materials. Lead is the traditional one Code 4 is the recommended thickness but this can be difficult to dress down over polycarbonate. Self-adhesive bitumen-based flashings stick well to plastic. These are used all too commonly in conservatory roofs but not always successfully. A good width that will dress over the joint by 100-150 mm either side is needed. A preformed plastic flashing that has been specially designed for use with a polycarbonate roof is preferred.

Fascia fixings
On a bungalow, your conservatory roof may have to connect with the existing fascia, rather than the wall below it. In these cases, aluminium extruded fittings can be fixed to the bottom of the fascia to support the roof sheets. The polycarbonate sheets will run in beneath the eaves where they need to be sealed against the wall.

Supports (not self-supporting systems)
If you’re using rafters to support your sheets your glazing bars will run down them and be fully supported along their length, screwed down at 400 mm centres.

If you have purlins, timbers that run horizontally across the roof, you’ll need to screw the bottom half of the glazing bar to every purlin and let it span the gap between them. The maximum span you can do this is 1500 mm but it makes for a stronger roof if you cut this down and limit the purlin spacings to 1000 mm. You need to use screws with plenty of bite that will sink in to about half the depth of the rafter or purlin. Stainless steel are best to avoid corrosion.

Side trimming
With the glazing bars fixed, the side trims or flashings can now be added. Some trims are pre-drilled to accept screws, with oversize holes to allow for some expansion movement.

Fixing the sheets
Polycarbonate can be scratched quite easily and is usually supplied with a protective film attached. Leave this film on for the most part but peel it back at the ends only, as you need to check that you’ve got the end with sealing tape, not the breathable tape, uppermost.

Run a bead of clear silicone mastic along the side flashing (or verge trim) and push the sheet into this and into position. The sheet’s other edge and vertical rib should engage with the glazing bar. The sheet needs some careful positioning to allow for thermal expansion and you should look for a 10 mm gap at the top from the wall and a 3 mm gap at the sides when you fix the side flashing. The side flashing should be fixed before you add the second sheet to the roof.

You can dress the flashing at the top now to this sheet (while you can get at it from the inside) although this is a job that needs to be done in stages, overlapping at each sheet if you don’t want to be clambering over the roof when you’ve finished.

Add the second sheet to the glazing bar and place the cover strip over the two edges. These pieces usually snap-lock into place with a little encouragement from a rubber mallet. They are down fully when the edge seals are pressing firmly against the polycarbonate sheet. Once the sheet is down, move up to the flashing for this section and proceed in this way until you reach the other side. Before this last sheet goes on the other side, the flashing (edge trim) needs to be fixed in place. With the sheets down, cover strips locked and flashings completed, the protective film can be removed from the sheets and they can be given a bit of a clean with soapy water and a sponge.

Glass roofing
Before the advent of double-glazing, all conservatory roofs were glass. Once glass safety became an issue and BS:6206 arrived, the only suitable glass for roofing became Georgian wired. As a cast plate it had the obscured finish that allowed it to be used in the windows of public toilets. Georgian wired glass is still produced but more commonly as polished plate glass of fine clarity. Technology has moved onto toughened and laminated safety glass that comes without any apparent difference in its appearance to ordinary glass. Glass above head height can give some people the jitters and for it to be safely installed there are some basic rules to be observed, the first being how it is to be supported. Glazing bars for most conservatory roofs run down the length of the roof supported on rafters and this two-edge system with the panes in one piece is often all that is needed. If there are unsupported edges at the ends because of the length of the roof slope, these will need to be stepped and flashed against windblown rain penetration. The four edge system of glazing picks up these ends with extra glazing bars so each pane is supported on all sides. With bars horizontally placed across the roof, provision has to be made for drainage, and the system needs some careful design, given the roof pitch and spans of panes and bars. In any case, patent-glazing systems shouldn’t be used below a pitch of 15 degrees.

Toughened glass used for roofing should be of the heat-soaked variety which the makers can guarantee against the risk of spontaneous fracture. Ordinary toughened glass fractures into a mosaic of tiny pieces that in vertical panes mostly stays put. But in a roof with gravity working against it, these pieces can shower down and cause injury to people below. Usually glass breaks because it has been badly installed or mishandled and these days with strict quality control procedures in the manufacturing process, material flaws are rare. Heat-soaking glass eliminates the risk of defects at the edges or from nickel sulphide, by exposing the material to high temperature levels for timed periods.

Self-cleaning glass
You also need to give some thought to how the glass will be cleaned. Hydrophobic coatings are not going to replace window cleaners, but by reducing the surface tension of the glass, they can stretch out the intervals between cleaning. The rain itself helps to wash the window or roof sheet.

Roof ridges and capping
The capping on a “glazed” roof is the weathering cap that covers the joints in the glazed panels: with polycarbonate roofs this is always PVC-u and quite often a bit on the chunky side. Some conservatory manufacturers have taken the trouble of slimming down the rafter pieces and caps on their Victorian style range to mimic the style of the era. The capping system has been taken on one step further with ventilated ridges and hips that provide exhaust ventilation through weather-resistance slots covered by insect mesh, and although these vents aren’t large enough to compensate for an opening rooflight, for example, they do provide a passive background ventilation on a permanent and secure basis. The vents are controllable with slide close covers but the point is to leave them open for seasons at a time. Trickle vents have been required in new-build windows since 1990. In aluminium systems the rafters are capped by glazing bars that can be painted to the colour of your choice. The great advantage of aluminium framing in general is that if supplied in its factory-finish state it can all be painted with an appropriate paint system to your own choice of colour.

Adjustable pitch ridges are often made that can cope with the typical low pitches of 15, 20, 25 & 30 degrees that are common to most conservatories. Ridges are for the most part, one of two designs; the plain cap ridge or the “Victorian” ridge of decorative pointy detailing that terminates in an even more decorative and pointy finial piece.

Glazing systems
When a lightweight polycarbonate roof material is used, the rafters are often omitted in small conservatories and the glazing bars that support the sheeting act in their absence as a kind of “self-supporting” system. In a lean-to conservatory, a wall plate section of PVC-u or aluminium is secured to the existing wall of your home and a proprietary eaves beam does the same job at the eaves end. Between them span the glazing bars but only up to a point. Both the eaves beam and wall plate are rebated to house the polycarbonate sheets in their standard thicknesses and at the sides of the roof (the verges) end bars cap the edge of the sheets.

If PVC-u doesn’t sound durable enough, some elements are available in aluminium. If that doesn’t to it for you timber rafters can be installed in a traditional roof to support the aluminium glazing bars complete with PVC capping. With this construction much greater spans can be achieved.

Traditional rafters
In the roof structure the timber is usually sawn material used for rafters. This can be painted, stained or varnished as required. With traditional lean-to roofs, the rafters have to be supported on the existing wall and this is done by either building in the timbers individually to cut-out pockets in the wall or by securing a wall plate to the wall using expansion or resin-anchor bolts and nailing the rafter ends to it. The plate need only be a similar size to the rafter and can be levelled to ensure a perfect roof level before being fixed into place.

Ordering structural timber
There are specific requirements for timber used in construction, particularly in the case of structural members whether they are used in floors, roofs or walls.

Grading
There are many strength grades for timber ranging from the weakest softwood to the strongest hardwood. You should ensure that roof timbers in sun lounges and garden rooms are at least “DRY” graded. This doesn’t mean they will actually turn up dry but that their moisture content is limited to a maximum of 24% Every piece of structural timber must be stamp-marked to say what stress grade it is – DRY or KN (kiln-dried).

You should quote KN grading for conservatory roof timbers because these may be subjected to rapid drying out beneath the glazed roof, and if they have a lot of moisture content to lose, this will cause them to shrink and split.

Preservative treatment
This should be requested on ordering as a pressure/vacuum treatment for protection against fungal and insect attack. Timber treatment can be done yourself with some products. All timber preservatives contain harmful chemicals and treatment should be undertaken with extreme care and protective clothing on.

Selection
Before accepting the delivery of any timber, check it for splits, shakes, knots and any bent or warped lengths. Reject anything unsuitable before signing the delivery ticket or paying. Look for the trademark of the FSC (Forest Stewardship Council)

Finishing touches
It is often worth adding some detailing to the eaves or ridges of roofs; timber mouldings have always been available for cornicing or dado rails. Most of these will serve well as coving details for the inside of the eaves beam beneath the roof, but if you can’t bear to include real timber or MDF in your plastic “paint-free” room, some of the plastic extruders now also produce fancy bits to personalise your new space. Given that you can’t decorate a glazed roof much beyond hanging a ceiling fan from the ridge, any styling along the line of the eaves is a focal point that is much appreciated.

Lead coverings
For small bay garden rooms, orangeries or additions to Georgian homes, lead is often the best alternative to glass for the roof material, as the two materials always go well together.

Lead is a soft and malleable metal that can be dressed to glass, masonry and timber, making it as common today as it was centuries ago. It does have a nasty habit when it’s new of leaching out carbonate when it gets rained on, and staining anything below it white; this is called patination, and the only way to prevent it is to seal the metal with patination oil as soon as the lead is installed. Because it expands and shrinks beneath the sun, lead has to be laid in relatively small pieces; on roofs, this means cutting it into bays and finding a way of joining them. The method of choice is often the lead roll, which you may have seen running down the slope of a roof towards the gutter. Not just functional but decorative as well, rolls have a wood core shaped like a handrail that is screwed down to the decking material, with the lead from each side dressed up and lapped over it.

Because lead can be dressed over glass rather neatly, it can be jointed with it, which means that you can have the top half of a pitched roof covered by lead sheet and the lower half glazed. There is no other material that this works so well in as lead, and even when the solid half is tiles or covered by slates, the joining of the two materials can only be done effectively in leadwork. Laying lead sheet is a skill that comes with training and experience.

A lead sheet roof can be applied to a pitched roof or flat roof: the only difference comes with the lapping of joints to maintain the weather resistance at different pitches. To keep the wind from lifting the roof up at the joints, clips made of copper or stainless steel are used. Nails can be used to pin lead sheets down to a timber-boarded deck while the clip holds the lapped joint in place and is used for roof pitches over 30 degrees. It’s common practice to stagger the continuous clip joints for each bay so that you don’t have to wrestle with the added problem of jointing them up at the meeting of bays.

Flat roofs
Flat roof structures are the simplest of all roofs to build but perhaps the least economical. The joists will only span so far and with the load on flat roof s equalling two-thirds of that on a floor, they remain quite large sections of timber. There is also one major drawback, which comes from insulating and ventilating flat-roof structures. Lagging them between the joists with glass fibre is no longer an option, as the depth for insulation and ventilation required prevents this from being possible. To achieve the necessary standard you must look to insulating with high-performing materials such as polyurethane foam board. 18 mm is the recommended thickness for robustness.

The alternative to this form of warm roof is a cold roof using thinner multi-laminate foil type insulation that is made up of several layers of aluminium foil, phenolic foam and thin quilt which together are less than 25 mm thick but achieve excellent insulation values. Larger spans may need to be justified by structural design calculations and may well need supporting beams to carry them.

If you plan to use your flat roof as a deck or balcony it becomes a floor and floor joist tables should be referred to.

Ventilation and shade
With a transparent roof and mostly glazed walls, your conservatory has a tremendous ability to absorb solar heat. It is vital that you consider the aspect that yours will have and what shade, if any, it will enjoy. East and west facing conservatories are ideal but ones exposed to the south will mean designing in some shade and good ventilation; tinted glass for example can be used in the roof to reflect the power of the sun or you may prefer to limit the extent of glazing in proportion to a tiled roof. Airflow is important too and a roof vent will allow warm air to be exhausted out as well as relieving wind pressure inside the room that occurs when a window or door is open.