Hi Charlotte,
We have a one-story house with a full basement, wooden paneling on the long sides, and Mexican brick on the gables. We have recently replaced the roof, with new felt and tiles on the existing roof boards. We have also installed a geothermal heat pump and an HRV system. Due to radon, the basement is slightly more depressurized than the entry level to prevent radon from being drawn up from the basement.
The ceiling towards the attic, according to the technical description and spot checks, is constructed as a 3/4” panel with 5+10 cm mineral wool as insulation, with some sawdust also underneath. The attic itself is completely unfinished with vents in both gables, a cold chimney in the middle.
No ventilation in the eaves or ridge.
Regardless, the attic now has, I assume, both less moisture from below thanks to the HRV but also less heat during the cold season due to the heat pump.
A common method for additional insulation in our case seems to be to remove the existing insulation, add a layer of new insulation with a vapor barrier underneath between the rafters. We have space for a total of 200 mm without extending the rafters.
But, if we choose to insulate the inside of the roof instead, we do not need to remove the existing insulation and can use the new material to insulate the roof with an air gap and get a warmer attic that provides insulating effect both downwards in living spaces and also for the HRV ducts.
I think it is partly easier to get the vapor barrier tight against the roof than against the ceiling where there are already a lot of penetrations, attic hatch, and similar, and partly that it will be easier to inspect possible new air gap than under new insulation.
Does it make sense to insulate the inside of the roof instead of the attic floor and leave the existing insulation in the attic floor as is?
We are not looking to furnish the attic, just achieve good additional insulation.
I have measured outdoor air coming into the HRV unit and the temperature just above the attic floor during January-February, and with 20 degrees indoors, around 0 outside +/- 5 degrees, there is a difference of about 5 degrees between the attic and outside. Does this give a hint of the saving potential?
The question then is how much I need to leave uninsulated towards the ridge for the gable ventilation to still be effective but also achieve the best possible insulation effect?
Should I stop the insulation at the height of the collar ties or also insulate between the collar ties so that there is a small attic above the insulation with gable ventilation?
Best regards,
Roger
We have a one-story house with a full basement, wooden paneling on the long sides, and Mexican brick on the gables. We have recently replaced the roof, with new felt and tiles on the existing roof boards. We have also installed a geothermal heat pump and an HRV system. Due to radon, the basement is slightly more depressurized than the entry level to prevent radon from being drawn up from the basement.
The ceiling towards the attic, according to the technical description and spot checks, is constructed as a 3/4” panel with 5+10 cm mineral wool as insulation, with some sawdust also underneath. The attic itself is completely unfinished with vents in both gables, a cold chimney in the middle.
No ventilation in the eaves or ridge.
Regardless, the attic now has, I assume, both less moisture from below thanks to the HRV but also less heat during the cold season due to the heat pump.
A common method for additional insulation in our case seems to be to remove the existing insulation, add a layer of new insulation with a vapor barrier underneath between the rafters. We have space for a total of 200 mm without extending the rafters.
But, if we choose to insulate the inside of the roof instead, we do not need to remove the existing insulation and can use the new material to insulate the roof with an air gap and get a warmer attic that provides insulating effect both downwards in living spaces and also for the HRV ducts.
I think it is partly easier to get the vapor barrier tight against the roof than against the ceiling where there are already a lot of penetrations, attic hatch, and similar, and partly that it will be easier to inspect possible new air gap than under new insulation.
Does it make sense to insulate the inside of the roof instead of the attic floor and leave the existing insulation in the attic floor as is?
We are not looking to furnish the attic, just achieve good additional insulation.
I have measured outdoor air coming into the HRV unit and the temperature just above the attic floor during January-February, and with 20 degrees indoors, around 0 outside +/- 5 degrees, there is a difference of about 5 degrees between the attic and outside. Does this give a hint of the saving potential?
The question then is how much I need to leave uninsulated towards the ridge for the gable ventilation to still be effective but also achieve the best possible insulation effect?
Should I stop the insulation at the height of the collar ties or also insulate between the collar ties so that there is a small attic above the insulation with gable ventilation?
Best regards,
Roger
Byggnadsingenjör
· Skåne
· 1 458 posts
An important consideration when adding insulation on top of existing attic flooring is to ensure air can circulate underneath the roof decking across the entire interior of the roof. This is achieved by installing a baffle with spacers, using materials like oil-hardened hardboard, specially treated paper, inorganic fabric, or similar.
It's advisable to have a hygrometer in the attic to ensure humidity levels do not exceed critical levels.
Adding insulation from the. inside. can be a solution to effectively manage the vapor barrier. However, this approach is not recommended if the ceiling height is already at 2.4 m. A. lower ceiling height can cause issues with ceiling lights and is likely to reduce the property's resale value.
It's advisable to have a hygrometer in the attic to ensure humidity levels do not exceed critical levels.
Adding insulation from the. inside. can be a solution to effectively manage the vapor barrier. However, this approach is not recommended if the ceiling height is already at 2.4 m. A. lower ceiling height can cause issues with ceiling lights and is likely to reduce the property's resale value.