Sunroom, glass extension and skylight

An extension with a lot of glass nearly always comes out of the same wish: more daylight, and the feeling that the garden belongs to the room. The route there differs. One person asks for a sunroom, another for a closed extension with a skylight in the roof, and a third only knows that the kitchen is dark and that it cannot stay that way. I build all three. So with me the conversation does not start at the material but at the use: in which months are you going to sit here, and what for?

Sunroom, veranda or glass extension: the difference

Those three words get mixed up, so let me pull them apart first.

A veranda is a canopy. A roof on posts against the back wall, open at the sides or with sliding panels you close up in autumn. It belongs to the garden, not to the house. You sit under it out of the rain and you use it mostly in spring and autumn, but it is not heated living space.

A sunroom is an enclosed space, with glass as the main material. Glass walls, and usually a glass or largely glass roof as well. You step straight into it from the living room or the kitchen.

A glass extension is, in building terms, simply an extension, with the same floor, the same heating and the same finish as the rest of your house, only with a back wall that is largely glass and often with a skylight in the flat roof. The difference from a sunroom sits less in the look than in what is asked of it: a space that is going to belong to your house has to insulate like living space too.

If you want the opposite, a closed extension with ordinary walls and one large glazed screen, that belongs with extensions and annexes. That page sets out what an extension involves, whatever amount of glass goes in it.

An insulated sunroom or a cold sunroom

This is the choice that decides the most, and at the same time the choice that gets the least thought.

A cold sunroom is not heated. Simpler glass, no insulated floor, no heating carried through. It is quicker to build and less disruptive. You probably know what follows from someone else’s sunroom: on the warmest days you do not sit in it, in winter you do not either, and on cold mornings the glass is covered in condensation on the inside.

An insulated sunroom is a real room. Insulation under the floor, insulating glass, attention to the draught sealing and to the point where the new space meets the existing wall, because that is where the cold creeps in if the detail is not right. Then you can sit there all year.

One thing I always add, because it gets forgotten. If you take out the existing back wall and pull the sunroom into the living room, you have not gained a room. You have one larger space that you have to heat as a whole, with a sizeable area of glass in it. Keep doors between them and you can shut the sunroom off in the coldest weeks and keep that choice open. It looks less handsome on a floor plan and it is a good deal more pleasant in February.

A skylight in the flat roof over the kitchen

Most enquiries that start with the word skylight are about the same house. A kitchen at the back, an existing extension with a flat roof, and a middle of the plan where no daylight reaches. An extra window in the wall does not solve that, because that light does not come far enough inside. Light from above does.

In building terms that is work on your roof, not on your wall. An opening goes into the roof structure, and that opening has to be carried, so extra timber or steel goes around it. On top of that comes an upstand, and on that upstand comes the skylight. The real work sits not in the glass but in the junction: the roof covering has to run up against that upstand and be finished watertight there. When a skylight starts to leak, it is almost never the glass. What I do on that roof side is on the page about roofing and roof coverings.

Think as well about what is in that ceiling now. An extract duct, electrics and sometimes pipework run exactly where you want the hole. You only see that once the ceiling is open, so I allow for it in the planning instead of pretending it does not happen.

The drawbacks of a skylight

I would rather deliver a skylight you are happy with than a skylight you simply have put in. So here is the honest list.

Heat in summer. Glass in a flat roof sits almost square to the sun when the sun is at its highest. With nothing done about it, the spot under your skylight becomes the warmest spot in the house, and in a kitchen where cooking goes on as well you notice that straight away.

Heat loss in winter. Glass always insulates worse than a closed, insulated roof surface. However good the glass is, a skylight stays a weaker point in your insulation envelope. The bigger you make it, the heavier that weighs.

Condensation. Warm, damp air from cooking and showering meets a cold surface and settles on it. On a flat surface you see that sooner than on an ordinary window. Good ventilation and an extractor hood that really vents outside make more difference here than the choice of glass.

Dirt. Horizontal glass does not rinse clean in the rain the way a vertical window does. Dust, leaves and grime stay put, and you look up at it every day from below.

Noise. Rain, and hail in particular, on glass you hear. One person finds that pleasant, another turns the television up during a shower.

Glare. Bright light straight from above is fine over a dining table or a worktop, and a nuisance over a television or a desk. So where the skylight goes is a choice, not a result of where the hole happens to fit.

What works against those drawbacks. Shading on the outside, because that is the only measure that stops the heat before it is inside. Shading on the inside softens the light, but by then the heat is already in the room. Solar control glass helps too, only it always costs you some daylight, exactly the daylight you did it for. And the simplest measure is the one most often skipped: do not make it bigger than it needs to be. Two smaller skylights often give enough light with less of everything listed above.

I advise against a skylight when the space already has glass on more than one side, or when the room faces south and there is no room in the plan for shading. Then you build in a problem you cannot get back out afterwards.

A timber sunroom annexe

Timber as a structural and visible material suits an older house and the garden side of a house well. It is also the work I feel most at home in, because I do carpentry and fitting every day.

Be honest about what timber asks for. It works, it moves with the weather, and it needs upkeep, certainly on the side that catches the sun and the rain. The difference between a timber annexe that ages well and one that rots sits in the details: no unprotected end grain, enough overhang, and nowhere any contact with the ground or with water that stands. That is not complicated, but it has to be thought through and carried out properly from the start, because repairing timber that has already gone wet seldom turns out well.

The floor and the junction with the rest of your house

The floor deserves separate attention. In a sunroom or a glass extension there is often tiling, because that stands up to sun, damp and dirt from outside, and sometimes with underfloor heating beneath it. The junction with the existing floor has to be level and the height has to be right, or at the threshold you see exactly where the old house stops. How I go about that is on flooring and tiling. If more changes, for instance because the kitchen moves or the whole layout is turned over, this belongs with a full renovation and I plan it as one job instead of as separate pieces that get in each other’s way.

Permits and structure

Behind your house a certain amount is often allowed without a permit, but that depends on the depth, the height, the size of your plot and whether you live in a protected townscape area. I think through with you what can and cannot be done before we start. If something structural changes, for instance because part of the back wall or a load-bearing wall has to come out, a structural engineer comes into it. The application itself runs in the owner’s name, so you submit that yourself. I supply the supporting information.

How it goes

I work on my own, over twenty years in the trade, out of Nieuwegein. Besides my own area I also work in Utrecht, and the distance to most towns in the region is short enough for me to come back for half a day as well.

You send me photos of the spot and tell me what you have in mind. I come and look, measure up and say what I would do, even when that is something other than what you asked for. After that you get a quote setting out what I do, what I supply and where the uncertainties sit. If you are still turning an idea over and do not yet know which way it should go, put your plan to me first. I will tell you honestly whether I would build it that way.