Ask This Old BT - Whole house fan

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2012-03-08 1:09 PM

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Subject: Ask This Old BT - Whole house fan

This is the second of what may be many older home maintenance/repair/update threads. My wife and I just bought a 60 year old house and I've got quite a few projects in mind.

One project is to remove the very old and very loud whole house fan, use the hole in the ceiling for pull down stairs, and add some plywood flooring to create additional storage space. I'm not doing the whole attic, and I do realize there are weight restrictions on what are essentially the ceiling joists of all the upper bedrooms and hall. That said, I've got some "as long as I'm up there" questions:

1. Should I cover/remove the large vent in the attic wall? I think so, but don't want to trap moisture up there. There is at least one smaller vent.

2. Should I staple some batting up on the roof joists? Seems like a no brainer since there is none there but maybe there is none there for a legit reason. Again, I want proper ventilation and don't want to trap moisture

 **I realize some folks will want to offer advice against removing the fan, and I do appreciate that point of view, but I really want to know specifically about the vent removal and addition of insulation.

2012-03-08 1:57 PM
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2012-03-08 2:31 PM
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Subject: RE: Ask This Old BT - Whole house fan

For attic spaces, ideally you need an in vent and an out vent for air, the in vent is usually, in newer houses, under the eavers, and the out vent is just a couple of roof vents. The attic should also be a cold space where air moves through smoothly. If you add any batting or insulation to the ceiling/roof in the attic you have the potential to create a hot space that traps hot air which traps moisture which leads to lots and lots of potential problems (mold, rot, etc). Their should be adequate insulation in the floor of the attic (Ceiling of the floor below) to keep the lower rooms warm.

Personally I would not cover the large vent unless there is a lot of adequat ventilation (check local regs for the square foot requirement for venting in attics but it is usually more than you would think). I do like the idea to create attic access and storage though so I would say do that, add the plywood, and store you christmas and camping stuff up there

2012-03-08 2:39 PM
in reply to: #4087122

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Subject: RE: Ask This Old BT - Whole house fan

There is some other ventilation but I'm not sure if it's ridge vent. I'm 99% sure there are no soffet vents.

There is old insulation between the "floor" joists, which are essentially the ceiling joists for the rooms below. I didn't know if top and bottom insulation (attic "ceiling" and attic "floor") would be overkill or would actually be helpful.

I do plan to do a better job with verifying ventilation, but I don't think I need a 3x3 vent on the side of the house. 

2012-03-08 3:04 PM
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2012-03-08 3:16 PM
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Subject: RE: Ask This Old BT - Whole house fan

There are two ways to do an attic.  As conditioned space or as unconditioned space.

When the space is conditioned, the floor usually doesn't have insulation, but the roof does.  Ventilation happens along the inner face of the sheathing.

When the space is unconditioned, the floor is condition and the roof isn't.  Ventilation happens thorough out the entire space.

Either way, you need air to come in and go out.  Typically, with conditioned space, air intake is from a soffit vent and exhaust is a ridge vent.  Typically (historically), with unconditioned space, air intake and exhaust are gable vents/louver panels.



2012-03-08 3:31 PM
in reply to: #4087355

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Subject: RE: Ask This Old BT - Whole house fan
scorpio516 - 2012-03-08 4:16 PM

There are two ways to do an attic.  As conditioned space or as unconditioned space.

When the space is conditioned, the floor usually doesn't have insulation, but the roof does.  Ventilation happens along the inner face of the sheathing.

When the space is unconditioned, the floor is condition and the roof isn't.  Ventilation happens thorough out the entire space.

Either way, you need air to come in and go out.  Typically, with conditioned space, air intake is from a soffit vent and exhaust is a ridge vent.  Typically (historically), with unconditioned space, air intake and exhaust are gable vents/louver panels.

Really sounds like I've got unconditioned for my attic.

I appreciate all the helpful input guys. I'll be verifying the total ventilation picture, but it looks like the large vent may need to stay and I'll just go with new batting on the floor and none for the roof

2012-03-08 3:39 PM
in reply to: #4087386

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Subject: RE: Ask This Old BT - Whole house fan
mrbbrad - 2012-03-08 4:31 PM
scorpio516 - 2012-03-08 4:16 PM

There are two ways to do an attic.  As conditioned space or as unconditioned space.

When the space is conditioned, the floor usually doesn't have insulation, but the roof does.  Ventilation happens along the inner face of the sheathing.

When the space is unconditioned, the floor is condition and the roof isn't.  Ventilation happens thorough out the entire space.

Either way, you need air to come in and go out.  Typically, with conditioned space, air intake is from a soffit vent and exhaust is a ridge vent.  Typically (historically), with unconditioned space, air intake and exhaust are gable vents/louver panels.

Really sounds like I've got unconditioned for my attic.

I appreciate all the helpful input guys. I'll be verifying the total ventilation picture, but it looks like the large vent may need to stay and I'll just go with new batting on the floor and none for the roof

I have an unconditioned space and my goal is to stop the heat loss from the upstairs into the attic.  I have a gabled roof with a vent on the gable ends and a center vent along the top.  It seems to do OK but I would like to look at a solar powered fan to replace one vent so I can pull the hot air out. That will be project 208 on the growing list....
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