Sunrooms and conservatories are made in a variety of styles and shapes and you can choose one that will suit the style of your house and the area you have available. Before deciding on the site, check that there will be no problems with drainage, that there are no trees nearby whose roots might cause a problem and that the sunroom will get sufficient sun in the winter months. You also want to consider, before finally deciding on the site, the ease with which you will be able to put electricity into the sunroom. If you intend to grow plants in it, make sure it is not to far from a water supply, or consider putting a rainwater barrel close to it.
Sunrooms are relatively light weight structures but you will still need to prepare a concrete base and trench foundations for the walls. A patio is not a strong enough foundation. The base will need to be a 4 inch concrete slab, with a 2 inch insulation board laid on top of 3 inches of hardcore.
Start by marking the desired height of the sunroom floor on the wall of the house. Next measure the area of the completed sunroom and set it out with profile boards. Dig out trenches for the wall footings, 1 foot wide for a single brick wall or 1 foot 6 inches if you are having an insulated cavity wall. The trenches should be between 1 foot 6 inches and 2 feet in depth. Mix 1 part of cement with 5 parts ballast (or 2 1/2 sharp sand and 3 1/2 aggregate). Do not make the concrete too wet. Allowing for two brick courses below ground, pour concrete into the trenches up to this level.
Let the concrete set and then dig out the ground within the footings, allowing for the depth of the new base, concrete, insulation and hardcore. Lay some courses of bricks on top of the footings, so that you have a height of at about 6 inches above ground level, measuring from the outside. Once the mortar has set, fill the ground inside the walls with hardcore, compacting it well down. The depth should be approximat4ely 3 inches once it has been compacted. More than this is fine, but it should not be less. Cover the hardcore with two inches of sand. Make this as level as you can, raking it and smoothing it with boards and then using a spirit level to check. Press it down firmly by laying a board and walking along it until all the sand has been compressed. Over the sand lay a damp-proof membrane. The edges should overlap the brick wall. If it is a double brick wall with a cavity, they should overlap the inside course. Where the sunroom joins the house, the membrane should turn up the house wall by a few inches. Lay insulation board on top of the damp-proof membrane and finally pour in 4 inches of concrete â€“ the same mix as before - starting at one corner. Compress and level the concrete by using a plank stretched across it â€“ this needs two people. Tamp the concrete down with the plank, moving slowing across the entire length, tamping as you go.
While the concrete is setting, lay a damp-proof course along the tops of the brick walls and tie it into the house's DPC. Now complete the brick walls to the desired height.
Erect the frame units on the walls, following the manufacturer's instructions. Where the rafters meet the house wall, cut a groove into the wall six inches above the rafter. Dress a lead flashing into this groove and fill it with mortar. The lower end of the flashing should be dressed over the top of the rafter. Lead is a soft material, easy to work, but it should be dressed, that is, shaped, on the ground first and then taken up. Any gaps between the house wall and the sunroom should be filled with silicone sealant.
Finally, lay a screed of sand and cement on the floor to give a fine smooth surface. This gives a surface which can be covered, ideally with ceramic tiles.