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Basic insulation questions


Jbdeltoro's Avatar
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09-13-12, 10:14 AM   #1  
Basic insulation questions

Hi All,
I bought an old house (1920's) and I demolished all the partition walls and removed all the plaster and drywall of the perimeter walls, not insulation in the walls nor in the attic, now it is just the new framing inside and the siding around the house and the attic, I want to start insulating walls and the attic, according to what I have seen, I should insulate the perimetral walls with batt and then vapor barrier and then drywall, looks like this is ok according to all the opinions and forums I have seen, the problem is to insulate the attic, MAIN question: Should I follow the same procedure as in the walls, meaning from bottom to top: drywall, vapor barrier, batt insulation ?

Many Thanks for your help

 
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09-13-12, 10:32 AM   #2  
Welcome to the forums.

Yes, you are correct - the vapor barrier goes to the warm side of wall. In your case, heating is more of an issue than cooling, so the warm side of the wall is considered to be the inside.

Now, hang tight, as others may chime in on whether you should use batts or a VB at all.

 
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09-13-12, 10:50 AM   #3  
If you have all the perimeter walls open I suggest that you bring in a foam insulation company and have them spray 2-pound density closed-cell foam. It will air seal the walls and acts as a vapor retarder by itself. In your climate it will definitely pay in the long run.

 
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09-14-12, 07:50 AM   #4  
Thanks for your comments, My main concern is the attic, some people say no vapor barrier, only drywall, insulation and the open space inside the attic(the attic is ventilated), is this right? or I should install vapor barrier between the drywall and the insulation
Thanks in advance

 
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09-14-12, 07:59 AM   #5  
An outside surface is an outside surface, whether it's horizontal or vertical. I would put a VB between the drywall and insulation.

 
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09-14-12, 08:49 AM   #6  
Hi Jb,
in mixed climates it becomes a balance between air conditioning and heating. You location should be very much heating, therefore a vapor barrier on the warm side would be a good idea. In addition, consider mineral wool for your insulation. It is much denser and will perform better than fiberglass, less air infiltration. One example is Roxul and it should be common in Ca. If you can fit a layer in between the ceiling joists, flush to the top and then another layer across them you would cover the joists and reduce their bridging effect. Baffles at the soffit to reduce air flow effects on the ends will help even with the denser insulation.

If not the mineral wool, I would go with cellulose, low cost and can be filled to the desired depth. Blown in it also can do a great job with irregular spacing, common on older homes.

If your walls sheathing is boards with gaps, if it isn't covered with an air barrier under the siding I would recommend adding something from the inside. Air barriers like house wrap are designed to allow moisture to escape thus not a vapor barrier.

Bud

 
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09-14-12, 09:51 AM   #7  
I have two more questions on this topic:
1.- Difference between Vapor Barrier and Air Barriers, is there any?
2.- If I install plastic (poly) very common in here between the drywall and insulation in walls and ceiling, (acting like vapor barrier or air barrier) what is going to happen with the vapor coming from cooking in the kitchen and taking shower in bathroom, should I install a fan in the bathroom and a range hood in the kitchen to get the moisture out?

 
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09-14-12, 10:06 AM   #8  
Bathroom fan is a definite yes and the range hood might be as well - you want to remove as much excess humidity as you can. Moisture can pass through drywall, it and the inside surface of the vapor barrier dry to the room.

Vapor barriers stop moisture, air barriers stop gaseous movement. Air barrier outside the sheathing of your house in house wrap, vapor barrier on the warm side of the insulation.

 
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09-14-12, 01:31 PM   #9  
Does Vapor Barrier stop moisture going from inside to outside?
The siding does not have an air vapor under it , right now the perimeter walls are only the 2x4 and the wood siding, is it enough with VB inside?

 
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09-18-12, 08:11 AM   #10  
In your part of the world, average temperatures are around 22C.
So you are looking at all year round heating?
In this situation the water vapor that is produced in the home will always be moving outwards, water vapor always moves from hot to cold.
Therefore, you do not want water vapor created by cooking, washing, breathing, sweating etc; moving inside your walls and roof, where it will condense on the cold wood and can create mold and wood rot.

The best way to deal with this is to create a plastic water vapor proof box with sheets of polystyrene fitted over the inside of the frame, water vapor proof plastic sheet fitted over that followed by drywall.

It is important that all holes and cracks are sealed as the water vapor molecules are very much smaller that air and they can move through the smallest crack.

If you merely fit insulation between the 4x2s then the frame itself will conduct your heat outwards, it is therefore important that the frame is insulated from the warm wet air inside your home.

You can go the other way and fit fibreglass between the 4x2s this will allow the water vapor to pass though the drywall and the fibreglass to escape outwards through a rain proof membrane, of course you will loose a lot of your heat.

 
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09-20-12, 11:31 AM   #11  
Thanks Perry525, I think I am good to start working, when you say a "plastic water vapor proof BOX" means that I have to install the plastic on the subfloor(under laminate or wooden floor) to complete the box (ceiling, walls and floor)

 
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09-20-12, 12:37 PM   #12  
I have to disagree here:
<The best way to deal with this is to create a plastic water vapor proof box with sheets of polystyrene fitted over the inside of the frame, water vapor proof plastic sheet fitted over that followed by drywall.>

In the field of energy efficiency they have started to back off on everything being a pure vapor barrier. If a vapor diffusion retarder will do the job then it would be a better choice over a vapor barrier. This will explain it better:
Vapor Barriers or Vapor Diffusion Retarders | Department of Energy
Plus this:
BSD-106: Understanding Vapor Barriers &mdash; Building Science Information

There is another concern when doing a really great job of air sealing a home and that is maintaining the right amount of ventilation to maintain air quality and for any combustion appliances. Plus, if any of those appliances are natural draft, then we don't want fans and exhaust appliances pulling combustion byproducts back into the house.

Moisture control and ventilation need to become part of your project.

Bud

 
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09-21-12, 01:30 AM   #13  
Jb lay the polystyrene on the plywood, then the plastic sheet, then a fully floating, glued T&G oriented strand board floor.
Lay the floor last and seal round the edge with low expanding foam.

 
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09-22-12, 10:09 AM   #14  
Bud

The key thing about insulation and water vapor sealing, is that the people who do the work must understand how water vapor works and they must do their work properly.

There have been a number of well advertised failure, because the people involved didn't know what they were supposed to do.

Windows we see that double pane sealed windows are clear during the day and often covered in condensation in the morning, despite similar outside temperatures. Usually double pane will mist up around 8C outside. During the day the warm convection currents of air keep the glass above dew point. At night when blinds are closed the convection currents disappear, the space in front of the glass drops below dew point and condensation forms. Triple glazed windows stay clear to lower outside temperatures because they are better insulated.

The current thinking regarding insulation and walls is, keep the frame warm above dew point and condensation will not form inside the frame. Therefore, the insulation must be on the outside.

This is illogical as, it is hard to insulate an existing home on the outside and one ends up with many heat bridges and keeping the frame warm costs money. Plus insulating on the inside required less insulation, has butted joints, no gaps and the only heat bridges are the nails or screws that fix the drywall,result a more comfortable home that is warmer in winter and cooler in summer.

As heat always move to cold and water vapor also moves to cold and areas of low pressure, the natural flow of water vapor and heat is outwards. The trick is to block the outside cold with insulation so that the inner surface is warm above dew point.

To this point having some insulation in the spaces between the frame helps, but the frame is then the problem as it is in indirect contact with the cold outside and the warm wet air inside, plus water vapor molecules are so tiny they can pass through drywall, the frame itself and all the cracks , holes and gaps in the normal home. Heat is lost by conduction through the frame.

Covering the inside of the frame which is usually a simple rectangle, where the insulation on the walls is butted against the insulation on the ceiling and the insulation on the floor is butted and sealed against the insulation on the walls really works.

With a floating floor there are no heat bridges.

The best and simple form of insulation.

With the insulation on the ceiling and walls covered with a water vapor proof plastic sheet and all the joins sealed and with the surface of the plastic sheet at room temperature there is no condensation and the water vapor does not enter the wall.

Each of us breaths out 14 cubic feet of 100% water vapor saturated air every 24 hours, small children and active animals a bit more, old people less active a bit less...this amounts to about 2 teaspoons of water each. We add to that the water vapor from cooking, washing, drying towels etc an unknown quantity as everyone’s life is different and some have exhaust fans in the bathroom, utility room, kitchen, toilet, some open their windows.

Most of the time the air outside is colder and drier, but not always, and merely opening a window may not work as the temperature and humidity outside may be the same as inside, this usually happens in the summer, when the frame temperature is high and there is no chance of condensation. In winter it holds good and heat and water vapor move outside.

With bathrooms, utility rooms and toilets, the best exhaust fans are ones with a built in heat exchangers where there is no pulling of air from other parts of the home, these balance the air within the room.

Kitchens are different as powerful exhaust fans require carefully sized and located holes to provide the required make up air, without making the lady of the house cold in a cross breeze.

Fires and boilers are best when they have enclosed make up air supplies that do not pull air from within the home.

Moisture control and ventilation can be sophisticated or merely an open window.

 
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09-23-12, 09:07 PM   #15  
I have to install the plastic on the subfloor(under laminate or wooden floor) to complete the box (ceiling, walls and floor)
I wouldn't do that. Plastic sheeting over the dirt in a crawl space is recommended by some, but I've always found that adequate ventilation was sufficient without that.

What is the foundation made of, and how is the foundation separated from the rim joist and the wall framing? Installing a barrier to prevent moisture from traveling from an open-cell cmu or rock or brick foundation can be critical to controlling moisture, and mildew, in the walls.

Installing a vapor barrier above the top-floor ceiling has always been an option I've ignored, but I live in a warmer climate than you do. That said, increasing the ventilation in the attic has invariably reduced my heating bills, given adequate insulation. Insulation is only effective when dry. In your climate, I would reflect on my experience with needing to run humidifiers in the winter and with seeing ice form in the attic as part of deciding whether to poly the ceiling.

As you're working on this, do provide the right amount of ventilation to maintain air quality and for the make-up air for any combustion appliances, as Bud suggested. Failing to do that is not healthy for children and other living things.

 
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