Adding insulation to attic, no vapor barrier

[Tony_S]

Hi all,
I own a very old 100+ year old "sawmill shanty" farmhouse that has some type of rock wool or loose insulation laying up in the attic. It's only about 3" or 4" deep. I suspect it was put in sometime in the 1960's during an extensive remodeling done by my family when I was a mere toddler.
I want to add more insulation, but there is no vapor barrier under the existing stuff. It's laying right on the gypsum.
What's the consensus on leaving it as is versus pulling a fascia board and shoving all the old stuff out?
I'm torn because I know it's important to have the vapor barrier, but then think about how long it has been this way, so how much harm can be done....and it would be a whole lot easier to just blow in more on top without removing the old.
What say ye?
Thanks for any input.

Tony, in the Shenandoah Valley of Va...where tonight's low will be 14 degrees, with a wind chill of 8, and 2-4" of snow coming tomorrow!

 

[aczlan]

I am not an expert, but in the many attics I have been in I have never seen vapor barrier installed over blown in insulation in an attic.

Aaron Z

 

[bp fick]

Go up to your attic on a really, really cold night, say around 10F and look around the rafters and underside of the roof decking, using a flashlight.

If you see frost, or sparkle of frost, this is moisture freezing in the cold attic space. This is not good. Much of this depends on relative humidity of houses generally. Other factors come into play, as well. Are exhaust fans from baths vented into the attic, for example? Houses that are buttoned up extremely tight often have high humidity issues. Houses that "leak" air, suck dry, cold air in from multiple cracks, openings, drafts, etc and humidity is desert like.

Typically, attics of older houses are dry and frost free only because there is so much upward heat loss from poor insulation. It is critical that attic ventilation be greatly increased when insulating. Once R30 or R40 insulation is installed, without a vapor barrier, by just blowing, the frost will often appear.

Why? Because now the heat is no longer keeping it dry, but oft times, the vapor still rises into the attic where it freezes and shows as frost.

 

[bp fick]

Are you sure that loose insulation is non toxic? Many older homes were insulated with a poured rock that contained asbestos and other toxic substances. Be sure you know what it is before you start shoveling it out, if you decide to go that route. :thumbsup:

 

[inveresk]

Venting the attic is more important than the vapour barrier but the vapour barrier might be needed depending on what happens in the rooms below the attic.

Adding additional insulation in the attic means it'll be a colder space in winter. The colder a space is the more susceptible it is to condensation so adding more insulation means you will increase condensation risk. If you don't have good ventilation in the attic, the moisture in the space can build up and cause problems. So you will have to ensure the attic is well ventilated around the eaves, and at the ridge or through cross flow gable vents. That should help any trapped moisture to evaporate out. Make sure vents are evenly distributed around the building so there are no pockets where cold, damp air can lie. Over time, it could be a problem. Most codes have a formula for working out how much free area you need for ventilation so check the code in your area. They often have it online.

The vapour barrier itself is usually less important. Its purpose is to stop damp air migrating from wet accommodation such as shower rooms into the building cavities or other spaces where it might condense on colder, unvented surfaces and so cause damage over time. The vapour barrier keeps that wet air where it's generated and where a fan can conduct it to the outside.

If you don't have any wet accommodation below the attic space and you keep the rooms reasonably warm, then the relative humidity in those rooms will probably be around 55 - 65% so the air shouldn't have enough water content to pose a problem in the attic. But if you ever alter the building and add a shower room below the attic, you'd be well advised to add a vapour barrier to the ceiling of that room.

 

[Jimmy Joe]

We built our house in 2000 and after some research and talking to our dry waller decided to go without a vapor barrier. This is what we found and I think it makes sense. If you put a vapor barrier (plastic) on your walls, if moisture hits the vapor barrier and condenses the moisture will run down. If you put plastic on the ceiling the moisture will condense and be trapped between the plastic and the drywall and rot the drywall maybe even to the point of falling off.

The dry waller said they prefer no plastic and when they spray the texture they mix in a vapor barrier paint. Attic ventilation is very important, there are a lot of homes with no vapor barrier in the ceiling doing just fine and I'm sure yours will be too. It would be a mistake if you laid a vapor barrier on your existing insulation and added more. The existing insulation would be like a big sponge if moisture got to it.

 

[PILOON]

You say the wool is loose.
It will still be good, remove collect and bag it for re use.
While not perfection, carefully lay a vapor barrier over the rafters
tucking it snugly and try to seal all joints with the special red tape (venture tape t.m.)used for that purpose.
Go up and over each rafter, slit barrier to clear struts and venture tape to seal openings.

Not a fun job, but can be done.
Just hope you don't need to crawl the entire time!

Hint; Sheet of 3/4 ply cut into 16" strips X 8 ft make good planks to walk on and easy to move around.


IMHO, insulation with today's energy costs, is a very rapid return on investement, as much as 2-3 years, and very much more so if you DIY the job.

I would then add the wool batts to the thickness you desire and save the loose wool to fill any voids and generally scatter loose over the wool batts for extra insulation.
The loose wool will be close to the same R value as blankets so you can figure what wool you want.
Don't forget to allow the attic to vent and don't pack the eaves up tight to the roof.
They sell formed poly vents (kinda corrugated) to place between the roof deck and the attic 'floor' for that. Very cost effective!

An attic, well insulated, should be close to the outside ambient temp if it is well insulated and breathes properly.

If you don't use a vapor barrier, come cold winter the attic will be quite warm and your insulation could become a soggy mess all full of frost.
I have even seen mildew growing in gyprock ceilings as well as blackened rafters.

Since you have about 4" of wool, I'd consider 8" of wool batts with the wool scattered over the top and filling voids.

Wear a mask so as to not breathe the particles.
Some of that rock wool was asbestos based but either way it is very much an irritant.

Good luck!

 

[Tony_S]

This is exactly what I needed to hear and did not expect less from you guys here at TBN. Excellent responses!!:thumbsup:

Currently there is no moisture (aside from the living creatures) generated below the attic space as it is all sleeping area, but perhaps down the road I will add a sink and toilet upstairs to take the load off :laughing: the downstairs bathroom. I will take that added moisture into consideration.
Our primary heat is wood stove so it does stay quite dry throughout the house.
Ventilation in attic is poor at best due to having only 3 gable vents. I've had an ongoing project on the front of the house replacing windows and insulating, and it is currently wrapped and ready for siding, at which time I will have a vented soffit added.
I have no idea if the existing insulation is toxic, and as I said earlier, I think it was added in the 60's...at that age it could go either way and would be good to have it tested.
I will concentrate on venting the attic before adding any insulation and gather some in-person evaluations.

It's quite drafty in the house now, but I am slowly tightening it up and can see where moisture could become a problem. It has an old standing seam metal roof too, so I need to be sure not to get it wet inside!

Again, thanks for everyone's advice. I have learned so much from all of you over the years. Priceless I say...priceless!!

Tony

 

[MossRoad]

Are you sure that loose insulation is non toxic? Many older homes were insulated with a poured rock that contained asbestos and other toxic substances. Be sure you know what it is before you start shoveling it out, if you decide to go that route. :thumbsup:

That's a good point. Vermiculite comes to mind.

 

[Reverend Blair]

I'd go with a vapour barrier. Seal it up tight. Air always moves from warm to cold. Air always carries at least some moisture with it. Moisture always condenses out as air cools. Once that moisture ends up in your insulation, you loose the R-value, and it doesn't come back when the insulation dries.