Garden office too hot

[Notch7]

Modern buildings may have good insulation and be well sealed, but they often have minimal thermal mass.

Your garden office has almost no thermal mass. That means it will warm up quickly in cold periods. However when it is hot, there will be no thermal mass material to absorb heat and refuce temperature. As soon as the sun gets in through the window the heat will rise quickly.

Maybe during the day when you have the windows open, the flow of air makes it feel cooler. Once its shut up there is no air movement, apart from convection so the warmest air ends up high up, at head level.

 

[jonnypron]

forced ventilation (fans inward on the shaded side, outwards at ceiling height) during the night will cool it. However if it is made of wood and insulation it will not have much thermal store, so will heat up quickly when the sun comes out.

Maybe you can fabricate shades for the windows.

It has so called solar blinds, but I can feel the heat behind them. I think maybe some solar film on the glass will help too.

 

[jonnypron]

Air moving over a surface will cool that surface. A well insulated building with air circulating through it WILL be cooler than that outside. A windowless extension I am building at the moment is several degrees colder inside than the outside. There is a marked difference.

I think the windowless factor is the main difference here. I'm sure that's the reason for the extra heat. It's cooler when the door is shut than outside for some of the day until say afternoon, but I guess the insulation only holds the heat back for a certain amount of time... especially rock wool which isn't as good as the celotex.

 

[big-all]

dont forget the shown forecast temperature is the measured outside temperature and is in the shade and in still air
the temperature in the sun will be perhaps 50-100% more so with a small volume off air and mass you room will quickly warm up
how thick was the insulation you installed??

 

[JohnD]

It has so called solar blinds, but I can feel the heat behind them. I think maybe some solar film on the glass will help too.

if the blinds are inside the building, then they will absorb whatever heat they don't reflect, and it is then inside the room.

I was thinking of a shade or shutter on the outside of the building, so that any heat they absorb can escape to the outside air.

It's possible that close-fitting boards to block the entire window reveal, made of aluminium foil-covered insulating foam, would do a pretty good job, on the sunny side. They'd also cut heat loss in winter.

 

[jonnypron]

dont forget the shown forecast temperature is the measured outside temperature and is in the shade and in still air
the temperature in the sun will be perhaps 50-100% more so with a small volume off air and mass you room will quickly warm up
how thick was the insulation you installed??

it was 100mm rock wool in the walls, and 100mm celotex in the ceiling. (75mm celotex in floor)

 

[Notch7]

if the blinds are inside the building, then they will absorb whatever heat they don't reflect, and it is then inside the room.

Its true -internal blinds have very limited benefits. They reduce glare and some solar gain, but the air space between the glass and the blind heats up, convection causes the air to flow so you then have a type of radiator.

Hot countries all have external shutters. Thats why in France, Italy etc you often see the windows are open in -to allow the windows to open with the shutters still closed.

UK windows are open out as its the best way to stop rain getting in.

 

[big-all]

it was 100mm rock wool in the walls, and 100mm celotex in the ceiling. (75mm celotex in floor)

similar insulation to my to my 10x12' shed
outside was about 26-27 ish inside about 35 ish with lots off glass on the sw facing wall
i have an opening window in the ne corner for airflow
i actually designed with opening windows on all walls but once insulated just left the door and the corner window as sufficient
will do some measurements today for you to compare with