Best way to insulate 100 year old unfinished attic ceiling?

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Your HVAC unit in the attic is exhausting hot air in the summer. Your attic will need to breathe. It sounds like your attic is part of the strategy to vent to the exterior. Ergo, your attic is acting as part of the exterior. If you insulate the attic roof, you are trapping the hot air in the attic, that is, hot humid air in the DC summers. I am imagining the cold ceiling surface below will be the sweat layer. Think of what a cold glass with ice does in the hot humid air - it sweats at the point of contact to that hot humid air which is the glass surface.

Why do you want to insulate the attic? To insulate the conditioned indoor air within the house?
If so, it sounds like the insulation should go on the attic floor where the conditioned indoor air is below and hot attic/exterior air above. BUT, I'm a little worried about needing a vapor barrier. Depending on your climate zone, you might need a vapor barrier.

https://buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

This is gibberish. The HVAC doesn't exhaust hot air into the attic. The issue isn't heat, it's moisture. The linked article is good but it doesn't sound like you got it.

Heat is transferred from refrigerant to outside air between the compressor and expansion valve = hot air.
The latent energy in hot air has the ability to carry more moisture than cold air.

Most people situate their HVAC units on the exterior for good reason. Seldom in the attic. This attic is being used as an exterior shed for the unit.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Your HVAC unit in the attic is exhausting hot air in the summer. Your attic will need to breathe. It sounds like your attic is part of the strategy to vent to the exterior. Ergo, your attic is acting as part of the exterior. If you insulate the attic roof, you are trapping the hot air in the attic, that is, hot humid air in the DC summers. I am imagining the cold ceiling surface below will be the sweat layer. Think of what a cold glass with ice does in the hot humid air - it sweats at the point of contact to that hot humid air which is the glass surface.

Why do you want to insulate the attic? To insulate the conditioned indoor air within the house?
If so, it sounds like the insulation should go on the attic floor where the conditioned indoor air is below and hot attic/exterior air above. BUT, I'm a little worried about needing a vapor barrier. Depending on your climate zone, you might need a vapor barrier.

https://buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

This is gibberish. The HVAC doesn't exhaust hot air into the attic. The issue isn't heat, it's moisture. The linked article is good but it doesn't sound like you got it.

Heat is transferred from refrigerant to outside air between the compressor and expansion valve = hot air.
The latent energy in hot air has the ability to carry more moisture than cold air.

Most people situate their HVAC units on the exterior for good reason. Seldom in the attic. This attic is being used as an exterior shed for the unit.

Nowhere did the OP say the compressor was in the attic, just the air handler.

The problem with attics isn't that they get hot. It's that at night in the winter they get cold. Any moisture that leaked through the ceiling condenses.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Having your HVAC equipment outside of the insulation, as you do now, is bad. You're essentially heating and cooling the outdoors. The equipment can get damaged by freezing as well.

Many older houses have external packaged units containing the AC and furnace together. How would having the AC in the attic be any different that that in regards to your comments?

An AC in the attic is a poor choice obviously, due to condensation and leakage and accessibility, but curious how it would be different than a package unit with the evaporator coil outside in the box?

A packaged unit is going to be constructed to be outdoors. The air handler in the attic is constructed to be inside conditioned space. A ventilated attic is unconditioned space.

For most of the 20th century most people in construction thought it was OK to have basements and attics that were sorta-kinda inside the conditioned space, and sorta-kinda outside. And it was sorta-kinda OK to put mechanicals in those spaces, and if they froze in the winter you dealt with it then.

There has been a real change in the past 20 years or so in terms of what is considered acceptable (and code) in residential construction. It's now expected that there be a clear demarcation between conditioned and unconditioned spaces and that there be a continuous layer of insulation between them.

Thanks for the response. So outdoor package units are insulated around the evap coil I'm assuming then?

Correct.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Your HVAC unit in the attic is exhausting hot air in the summer. Your attic will need to breathe. It sounds like your attic is part of the strategy to vent to the exterior. Ergo, your attic is acting as part of the exterior. If you insulate the attic roof, you are trapping the hot air in the attic, that is, hot humid air in the DC summers. I am imagining the cold ceiling surface below will be the sweat layer. Think of what a cold glass with ice does in the hot humid air - it sweats at the point of contact to that hot humid air which is the glass surface.

Why do you want to insulate the attic? To insulate the conditioned indoor air within the house?
If so, it sounds like the insulation should go on the attic floor where the conditioned indoor air is below and hot attic/exterior air above. BUT, I'm a little worried about needing a vapor barrier. Depending on your climate zone, you might need a vapor barrier.

https://buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

This is gibberish. The HVAC doesn't exhaust hot air into the attic. The issue isn't heat, it's moisture. The linked article is good but it doesn't sound like you got it.

Heat is transferred from refrigerant to outside air between the compressor and expansion valve = hot air.
The latent energy in hot air has the ability to carry more moisture than cold air.

Most people situate their HVAC units on the exterior for good reason. Seldom in the attic. This attic is being used as an exterior shed for the unit.

Nowhere did the OP say the compressor was in the attic, just the air handler.

The problem with attics isn't that they get hot. It's that at night in the winter they get cold. Any moisture that leaked through the ceiling condenses.

AHU and ducting insulated?

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Your HVAC unit in the attic is exhausting hot air in the summer. Your attic will need to breathe. It sounds like your attic is part of the strategy to vent to the exterior. Ergo, your attic is acting as part of the exterior. If you insulate the attic roof, you are trapping the hot air in the attic, that is, hot humid air in the DC summers. I am imagining the cold ceiling surface below will be the sweat layer. Think of what a cold glass with ice does in the hot humid air - it sweats at the point of contact to that hot humid air which is the glass surface.

Why do you want to insulate the attic? To insulate the conditioned indoor air within the house?
If so, it sounds like the insulation should go on the attic floor where the conditioned indoor air is below and hot attic/exterior air above. BUT, I'm a little worried about needing a vapor barrier. Depending on your climate zone, you might need a vapor barrier.

https://buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

This is gibberish. The HVAC doesn't exhaust hot air into the attic. The issue isn't heat, it's moisture. The linked article is good but it doesn't sound like you got it.

Heat is transferred from refrigerant to outside air between the compressor and expansion valve = hot air.
The latent energy in hot air has the ability to carry more moisture than cold air.

Most people situate their HVAC units on the exterior for good reason. Seldom in the attic. This attic is being used as an exterior shed for the unit.

Nowhere did the OP say the compressor was in the attic, just the air handler.

The problem with attics isn't that they get hot. It's that at night in the winter they get cold. Any moisture that leaked through the ceiling condenses.

AHU and ducting insulated?

There's no good way to install an AHU in unconditioned space.

[Anonymous]

Thank you so much for this very helpful discussion! We really get that it is all about moisture thanks to your comments. OP here to clairfy:

1. Our goal is to finish the attic into living space.

2. It is correct - we have just the air handler unit in the attic and the compressor is outside. This is how it was when we bought our home.

3. Our current thinking is to wall the air handler unit into the conditioned space we are making. And use a smart membrane product like intello or membrain to prevent moisuture from reaching cold surfaces in the walls and rafters. Combined with an unfaced batt insulation.

What do you all think?

[Anonymous]

Anonymous wrote:Thank you so much for this very helpful discussion! We really get that it is all about moisture thanks to your comments. OP here to clairfy:

1. Our goal is to finish the attic into living space.

2. It is correct - we have just the air handler unit in the attic and the compressor is outside. This is how it was when we bought our home.

3. Our current thinking is to wall the air handler unit into the conditioned space we are making. And use a smart membrane product like intello or membrain to prevent moisuture from reaching cold surfaces in the walls and rafters. Combined with an unfaced batt insulation.

What do you all think?

Works. The fan and evaporation coil don't need anything special around them if the entire attic around them is insulated. That would be the same as having it in a closet in most homes. Would be good to make a little closet space around it to reduce the noise coming from it, though it will still be loud due to the air intake vents in a more confined space like the attic.

Just make sure to check and perhaps update the condensation drain lines.

[Anonymous]

Look up spray foam, attic and uninsurable. You could also look up unmortgageable but that’s a mouthfull.

Rockwool and you don’t need foam jockeys

[Anonymous]

Anonymous wrote:Look up spray foam, attic and uninsurable. You could also look up unmortgageable but that’s a mouthfull.

Rockwool and you don’t need foam jockeys

Op here, what would you suggest doing in this situation?

[Anonymous]

Anonymous wrote:Look up spray foam, attic and uninsurable. You could also look up unmortgageable but that’s a mouthfull.

Rockwool and you don’t need foam jockeys

Rockwool and you absolutely, absolutely need vent channels between the insulation and the sheathing. If the roof isn't already vented at peak and eave this may not be feasible.

If the roof can't be made to be vented spray foam is really the only solution. The other alternative would be foam on the outside between the sheathing and the shingles, but that would require re-roofing.

[Anonymous]

Anonymous wrote:Thank you so much for this very helpful discussion! We really get that it is all about moisture thanks to your comments. OP here to clairfy:

1. Our goal is to finish the attic into living space.

2. It is correct - we have just the air handler unit in the attic and the compressor is outside. This is how it was when we bought our home.

3. Our current thinking is to wall the air handler unit into the conditioned space we are making. And use a smart membrane product like intello or membrain to prevent moisuture from reaching cold surfaces in the walls and rafters. Combined with an unfaced batt insulation.

What do you all think?

A smart membrane is good, but it is in no way sufficient to protect the roof from condensation. You need either ventilation between the insulation and sheathing, spray foam, or insulation on the exterior.

[Anonymous]

Thanks! This is very helpful.

[Anonymous]

Anonymous wrote:

Anonymous wrote:
We have a HVAC unit that provides AC to our upstairs located in the attic.

old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go?

First of all, having an AC unit in the attic is horrible for moisture disaster issues, though that's a whole other project and big money to fix.

So the insulation that looks like shredded paper is called "cellulose" insulation, and it is made of, wait for it, shredded paper. Very cheap and poor quality insulation, but "green" aka a scam mostly. You will spend more in utility bills from its lower rating so it is not green at all.

Cellulose insulation also is a prime mold growth medium and attracts insects, as you have found out.

Fiberglass is what you seek. Blown in is cheaper and easier to do, batting is better and more costly, doing both is best.

Agree with everything but the conclusion (Rockwool beats fiberglass in every way) and would add don’t fall for borate treated cellulose either.

[Anonymous]

Don’t blow in anything. It’s as permanent and messy as it sounds.

Rockwool is more expensive but quite frankly you can install it with a butterknife and patience.

[Anonymous]

Anonymous wrote:

Anonymous wrote:Look up spray foam, attic and uninsurable. You could also look up unmortgageable but that’s a mouthfull.

Rockwool and you don’t need foam jockeys

Op here, what would you suggest doing in this situation?

Rockwool. They also have a great technical support line.

You could vent it — Home Depot sells different baffle vents.

There are some new hemp based products but not yet tested enough.

There is some, not a lot, good building science out there (mostly ignored):

https://www.energy.gov/eere/buildings/building-america-webinar-stump-building-science-chump-joe-lstiburek-text-version

https://buildingscience.com/documents/building-science-insights-newsletters/bsi-095-how-buildings-age