Kieran McCarthy: The conservatory is sucking heat out of the house. What should we do?
"The walls and the roof were made from glass, usually single-glazed. The issue here is that single-glazed glass will allow nearly all the heat to escape in winter and provide no defence against solar gain when the sun shines in summer."
Hello Christopher, Thank you for this timely question. Ah yes, the humble conservatory; a house design breakthrough dating back to the 1990s.
Back then, when the sun shone, the only way out was through the backdoor in the utility room. Then, with the arrival of aluminium and then, PVC windows (instead of the prevailing rotting softwood), people began to install a sliding door from the kitchen-dining area out into the garden. This helped a lot, but only when the sun was really shining.
But what about all those days when there is light but no heat (ie most of the time)? This is where the conservatory came in.
Finally, we could simply add a room to the back (or side) of our house where family gatherings and general leisure activities could take place. Bliss! Or was it?
Unfortunately, during the summer these glasshouses became like Scandinavian saunas, while in winter, they were like igloos. So, where did it all go wrong and how do we rethink this social hub and redesign it to suit all seasons?
The issue with conservatories was that while they catered for a vital social and leisure space in our homes, building design had not yet caught up with this new glazed extravagance. The ground slab was often just a concrete slab laid on a thin layer of insulation (if at all), and all laid in one day so no effort was made to prevent coldness from entering the slab from the edges and indeed much of the cold in the ground wasn’t kept at bay at all.
The walls and the roof were made from glass, usually single-glazed. The issue here is that single-glazed glass will allow nearly all the heat to escape in winter and provide no defence against solar gain when the sun shines in summer. This may be why you are generally losing heat through this room for much of the year. So, what can be done?
My parents have a conservatory and were experiencing the same issues you highlighted. Theirs, however, is outside the front door as it was originally part of the porch. They insulated and clad theroof (internally) and, though not ideal, this helped a lot with the seasonal use of this room and, as it is essentially outside of the thermal envelope of their main house, they don’t lose heat from the house to the conservatory in winter.
In your case, it appears this is not possible. To remedy this, I feel you have two choices: Either install a double-glazed sliding door between the house on the conservatory or, if the budget allows, knock and rebuild the entire extension.
If you were building a new sunroom, I would advise as follows: Get an engineer to draw up plans for an insulated concrete slab. Now you will be fitting 150mm of new rigid insulation beneath the floor with 150mm of concrete on top. You will fit 25mm of insulation at the edges of the concrete slab to ensure the slab doesn’t get cold at the edges.
I would add insulated blockwork walls built on thermal blocks (special blocks that have an insulating capacity) which, again, reduce heat loss to the ground and the outside. You can add in windows and a new sliding door to suit access to your garden and the light and views you wish to capture.
If you are investing at this level I would certainly recommend triple glazing. For a room this size it’s not likely a huge additional expense, but it will certainly provide a little more comfort in extremes of heat and cold.
Next, the roof. Here I would advise a timber-vaulted structure with a slated or tiled roof. The roof can be insulated with rigid insulation between the timber rafters and an insulated plasterboard slab placed internally to further prevent against heat loss at this level.
When this structure is plastered and finished internally and externally, you have a new sunroom, well insulated from the highs and lows of the seasons. The difference here is the attention to insulation. Just like a thermos flask, it keeps things cool in summer and warm in winter.
- Kieran McCarthy is a building engineer and director of KMC Homes bespoke A-rated new-home builder, serving Cork and Limerick. He is also co-presenter of the RTÉ property show Cheap Irish Homes.
- Follow Kieran on Instagram @kierankmc for more home building information, tips and Q&A advice.
- You can also follow Kieran on the Built Around You YouTube channel and @kierankmc on TikTok.
