Insulate the Attic Floor or Between the Rafters?

Thanks. I am considering changing the insulation, at least. The community has some strict covenants on what can protrude from the roof of the houses and facade facing the street. So, the challenge is adding a fan without it looking like I installed one (from the outside).

Hello PH,

I hope you are fine!

From several years experience in building, and even more in maintenance of all types of buildings, if your roof is slate or tiles you have no use whatsoever for a FAN in your loft. You do have a need for VENTILATION, so, if you have no 'ridge tiles' which are vent' tiles get a couple fitted now. They should be fitted as far away from the toilette vent' and bathroom vent' as possible, without being closer to your neighbours toilette and bath vent'.

A fan is a possible danger and, it is bound to be a cause of vibration.

Think about this, .......................... Do you know of ANY MANSION with a series of fans in the roof space? There is non! A fan is not needed. The temperature rise you mention in degrees Fahrenheit is, converted to Celsius just a couple of degrees and is more than the temperature rise built into the fabric of your house.

If you are worried about the air ventilation which keeps your home cool, do not bother to take any loft insulation out, just add to the insulation you already have and completely cover the vent tube, both on the loft floor and get some pre-formed insulation for the vertical part of the vent tube. This insulation will stop the ceilings from getting warm and radiating this heat to your rooms. As long as this is thick enough, it will also stop the vent pipe getting warm.

If in addition you have a vent pipe from the boiler which may go through the roof space, this should be insulated also.

You say and I am talking from memory of your first post, that you fitted a new air intake at eaves height? If the air is hot outside, this heat will be drawn through the vent pipe and blown through the rooms in your home, and the heat you think is coming from the roof space my in fact be coming from the air intake outside the house.

From the info' I glean from your last few posts, you plan on quite a lot of work to solve this problem, (as seen by you), where properly insulated vent and roof will stop this problem.

I have not seen you mention the fabric and make-up of your roof, and where you live and outdoor temperature? And forgive for this but, I have not had time recently to read back through the posts. You should not need to insulate directly under the tiles or slates, and if your roof is bitumen the insulation on the inside of the roof directly on the underside of the bitumen or similar, will allow your roof to heat up to a much high temperature and may even weaken the fabric by heat radiation back up through the roof fabric which makes the fabric 'soft', and could possibly weaken and reduce the 'life' of the actual roof covering.

You can 'test' this hypothesis if you have or can get hold of the same bituminous fabric. Get two pieces and support them on bricks or wood along two edges and inside a large cardboard box. (Which is a reproduction as far as is possible) of your roof and underside of it. Insulate with foil on the back of one piece and leave the other bare. You should find the insulated test piece will get substantially hotter.

=

Please forgive me if I am preaching to 'the converted' with any of the references above. I am just trying to save you work which does not need to be done and try and keep the fabric of your roof as good as possible so it will last as long as it was designed to do!

Take care................. No insult intended my friend. Please forgive the length of this post.

OK, just to be different, I'll give you another perspective. The correct answer may instead be: "it depends."

It is POSSIBLE to correctly apply Icynene or 2-part polyurethane expanding foam directly to the underside of your roof deck, sealing in the joist cavities. This is typically done in pole barns, steel frame structures, hurricane-region homes with rafters rather than trusses, and many other applications where there either is 'no' ceiling to make an attic, or where the attic will not - repeat 'not' - be vented.
This may be the case for you, should you choose to do it.

If your roofing is tile, slate, or steel, you have NO problem with any additional heat buildup that may or may not be problematic in the way that tar/asphalt shingles "could" be. Though really, I've not yet heard of a real shingle problem, only that earlier a few defective batches used to be blamed on unvented attics so the manuf. could get out of replacing them.

In fact, an UNvented attic space is recommended for energy-star rated applications where the roofing material is OK with that, and particularly when mechanical HVAC equipment is located - like your ductwork is located - in that attic space.

Even if you added mechanical venting (attic fans) or additional ridge vents and more soffit inlet free area, your attic will likely reach over 130 deg F on a hot day with shingles, so yes, this is adding to your electric bill, and you may well be a good candidate for properly applied attic/roof insulation.

Don't try it with batting - it would need to be a full spray-foam installation for sealing, vapor barrier, etc.

Oh - and it will "glue" your trusses to the roof decking as well, so you'll end up with a stronger structure that's highly wind resistant - or more difficult to rip out and replace, depending on what you're trying to do later... ;)

Thanks - If I do follow that route, I will be sure to sell the house 3 years before I need to replace the roof.

I have installed roll fiberglass in our attic space, 13 inches which brought it up to R42. We also have a structural roof of wood rafters and 1/2 inch CDX then steel roofing with vent line at the peak of 2 1/2 inch screened the entire length of the roof. With that we do not need additional vents in the roof or ends at the gables (we have 4 gables). We have done some of the engineering for an attic run heat pump air/heat system and found that the duct work in the attic will require insulating of 2 inch foil covered wrap, plus a lot of duct tape. The heat loss from the heat pump to the farthest end (70 feet)is calcullated to be 1 degree. It's the same for air.

Overdoing it is a waste of capital. Underdoing it is a waste of beer money. See your local supplier of ductwork he should be able to tell you what to install in ductwork insulation or see your local heat/AC guy., since we don't know all the details of your home, what type of ducting you have or efficiency of your air system. I'm sure they all have a book and if not see your power company. They have a new motto to save energy. And ask for the federal and/or state tax deduction info on whatever you do. Some states have one up to $4000.

You also might consider reflective barriers in the rafters. There are two types that I know of. One is an aluminum spray paint that is sprayed onto the rafters and underside of the roof. the other is aluminized craft paper that you staple to the rafters. Beware the spray paint if it gets onto your AC unit (make sure the contractor covers and masks all else).

I agree. I had a radiant barrier installed in my home and it makes a huge difference. Most claim a 30% reduction to electric bills to cool your home, which is probably close to accurate.

Hello PH,

Firstly, let me say welcome! You will find us a helpful lot and CR4 has some very clever people here.

Regarding your roof, you did not say if you have a tile or steel roof. Any heat build up would not matter if you have these as a roof?

It may be that the roof-space will heat up quite naturally during a hot day, and is nothing to worry about. Even if you do not have vents on the ridge, there in usually enough air able to get in via the slight gaps between the bottom of one slate and the top of another.

Are you sure that the heat build up is not air rising through your air vent ducting from inside your house?Insulate the duct, then see if there is a difference. The temperature you list is only ~ 3 °C MAX. I do not know where you live, but condition in Canada can vary enormously from the US or Europe.

~ 2-3 °C is nothing to worry about whatsoever. More insulation on the floor between the rafters and on the ducting will save you money in the long-run! Do not worry about the heat. If you were talking of 40 °C, then there would be a problem, but 2-3 degrees Celsius is well within limits.

Stop worrying and count your cash.............. saved by the extra insulation.

Take care.

Hi BB

I nearly pressed the send button publishing something I had prepared before but will take my time to give this one a go. I am aware of the problematic but my answer would breach confidentiality (non existing patent). I have a simple solution to the above problem and will have to phrase my reply really carefully, so not to offend other technologies and their merchants.

I'll work on it but will not be able to respond until the beginning of next week. I'm going were no communication is possible. No, not jail, but bush. Insulation is very much asked for and the Australian sun has no mercy. Arctic regions have a similar problem, just the other way around but I've covered that as well in may invention.

No takers yet? I'm not surprised, you have no idea how simple it would be to do some retrofitting. Nuff said, more info soon, Ky.

Hi ky,

That was like the preface to a good book.................. sorta keeps you wondering? You sure you aint telling porkpies and are actually spending time in 'der slammer'? You going to the 'bush'? .................. I was there last night. Highly recommended! What do you you dirty ba-sta-d? It is all in your mind! Good though innit?

Take care my friend and make sure you have the patent before publishing !!!

Hi BB

I have just come back to the "real world" and am following up on some loose ends. This thread is one of them. I will keep my silence on this one and only my enthusiasm has provoked me to my past remarks in this thread. I have advised my self from contributing in this thread in a exhibitionist manner and am sure, even more so, that my concept and applied technology is not to be published yet. Did you notice that I have not called any of the other posts as crap?

In short; If i were the person in charge of procurement (Procurement Officer, what a title![other wise called "the Bean Counters"]) I would not want to make the decision to ax established contacts and go with a cheaper better and more variable way of insulating than the existing methods. (Retro-fitting)

"I meet my contacts 4 times a year and we have a great time doing what we do best" (they say): "Jobs for the mates" we call it here in Australia. And we tell/accuse other Countries that they are corrupt? The only thriving business here is insulation. You receive a subsidy of $1600 if you retrofit your house with insulation but you have to use an established business(technology) to do so. This has again stopped me in my tracks and I am none the wiser for it. No, I do not wish to become the member of a political party and will leave it at that for the moment.

Speaking is silver, silence is gold. Just "you's" struggle, ignorance has never succeeded. My concept will!

Temperatures around here are moderate, at the moment that is! May "your's" choice of temperature fulfill its self, economically, that is.

See you next time, all the best, Ky.

Vent vent vent that attic space, fans are good too.

Use blow in lofting fiberglass or insulating wool add six inches over ducting then cover with four inches cellulose blow in

Hi wire,

Ref' post #10.....................

That sounds good to me! Can't really understand why the OP is worried about a 3 deg' Celsius temp' rise there though? Will they worry when it is near freezing or below in the winter?............

Take care.

If you want to get better ventilation, look into installing a ridge vent. It will give you more air changes without the use of power.

I would like to contribute to Sandman's opinion.

In the case that you are concerned about energy efficiency the only possible answer can be: More insulation!

In the case that the attic is unattended, it may be sensible to add insulation between the rafters and the roof, if space permitting. I would not be concerned about temperature increase on the roof material als the heat uptake will not change, neither the heat transfer to ambient (in steady state condition, of course!).

However, ma personal favorite would be to insulate the ductwork of the AC system. Depending on the constructin of the ductwork it might eve be possible to buy pre-formed insulation shells which will perfectly fit around the ductwork. Why not ask your installer?

In no case would I vent or "air-condition" the attic, as this will be far less effective that the insulation. Plus the power to drive the fan (s) will add up to your electrical power bill. Depending on the air flow conditions in the attic generated by a fan, it might even make the situation worse, as the heat transfer between the ambinet air and the ductwork will be increased by an increasing turbulence of the air flow (conditions without fan: natural convection only, conditions with fan: enforced convection. You can do your ow calculations, based on typical contitions in the attic).

Energy efficient regards

nudnik

I like to stick to the facts when it comes to insulating. What I understand is the more you insulate the more you need to ventilate. There is no such thing as too much ventilation.

I had Icynene sprayed in the walls and Cathedral ceiling of my house addition. My web searches showed different schools of thoughts on the need to ventilate the underside of the roof deck. Remember now that there is no such thing as too much ventilation. I installed ventilation baffles on 100% of the roof deck before the Icynene was sprayed.

Don't forget to close off the non vented area just under the baffles so the expanding Foam won't migrate into the overhang of the roof. Which also has 100% ventilation across the length of the house. There is also a ridge vent along the peak of the roof so take care in blocking the Icynene from getting into the ridge vent area. I now have a nice flow of air on the underside of the roof deck. The roof has fiberglass shingles.

Icynene is not a vapor barrior. So decide on what you will use to stop moisture migration from inside the house through the drywall to the outside. Foil backed drywall was my choice but the additional $1000 seemed a bit much at the time. I settled on Vapor barrior paint. I think it was a Benjamin Moore product. Time will tell if the Icynene stays dry. I think it will. The teperature in the addition stays more consistant than the original house.

GA! This is how our house was done. The flexible vent pipe was laid before the blow insulation was put in. I am not sure what type of blow insulation was put it. I would guess either wool or cotton fiber. It is about 10 inches thick in most areas and piled up over the vent pipe. It works very well!

Mee two

I all so aggree with oz

"ventilation will all so improve that..."...

Ya missed the MAIN point!

"If the duct work is not insulted very well..."

Tell that lazy no-good-fer-nuthin duct work that you mean business, and if it doesn't shape up and start delivering cool air right away you're gonna replace it with an ice chest and a fan!!!

That oughtta do it for now...

Got it - I need to issue a decree to change the laws of physics....

Hmmm... --- actually, I don't think you did get it.

Twarn't nuthin but humor. Pure, unadulterated humor, derived from the poster's failure to "[Preview]" / proof-read his post before submitting.

His post states that the ducts need to be insulted ... rather than insulated.

So, climb in that attic and commence bellowing!

Hi Guest,

This is not aimed at you, but as you and others mentioned 'ventilation', venting is fine, but do not confuse it with "circulation". Circulating warm air does not really do any good.

Take care.

thanks

Thanks, sounds like an interesting solution. Unfortunately, I am somewhat limited to what I can mount external to the house based on the community covenants.

One thing that I do not think was addressed, that is a common problem, is the blockage of soffit vents, resulting from blown-in insulation being blown past the plane of the outside wall, as well as other debris. Attic ventilation is most effective when a convection current is established, with air entering at the soffits (low point) and exiting at the roof, ridge or gable vents (high point). Check if these are blocked (if so, shopvac them out) and/or add vents, if possible.

Add more insulation to the attic floor.

Insulate your A/C vents, by wrapping or burying them with insulation.