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Author Topic: Attic with foil-backed plywood roofing question  (Read 2380 times)

WD2AJW

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Attic with foil-backed plywood roofing question
« on: June 28, 2019, 06:46:54 AM »

I live in Florida in a new home that was built with foil-backed plywood as roofing material. It does wonders for keeping our home cool but I'm thinking not so great for an antenna farm in the attic since our HOA doesn't allow antenna's outdoors.

Has anyone had any experience using an antenna in such an attic? I've read some posts in other forums where people have done it and claim no ill-effects of doing so but common sense is telling me it's not a great idea from both a technical aspect and a safety aspect, especially since the antennas would be right above occupied bedrooms. All the electrical wires for AC outlets, alarm wires and cat5 are also running through the attic since this is a one-story home.

Thoughts? Suggestions?
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K4FMH

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RE: Attic with foil-backed plywood roofing question
« Reply #1 on: June 28, 2019, 07:36:05 AM »

Yes, I have had foil-backed plywood as a radiator barrier with a ridge cap for 7 years in the home we built then. The individual plywood foil sections are NOT bonded and have a 1/4” or so gap for expansion and contraction.I have several antennas in my large attic. One is a horizontal(ish) loop run just under the edges of the shingles. Another is an MFJ 80/40 meter dipole. Inverted Vee dipoles for 20 and 15 meters ate mounted along the joist peaks. A Cushcraft D4 dipole is now gong up under the main joist (preliminary SWR sweep looks good). A Diamond X30 dual band antenna is mounted in another part of the attic. A Ventenna dual band antenna was installed over one of the roof exhaust pipes.

Now, here’s what I’ve observed over this seven year period. One of my first HF contacts was with a well known ham in Malibu CA using the loop. From central MS using 100 watts during the evening hours, I thought that was a good contact. The 80/40 dipole has worked similarly in terms of expected contacts given the time of day and band. These antennas and the D4 being installed now (slowly to avoid the 90+ degree days) do not seem to couple with the foil-backing, even the loop which is mounted the closest. The Ventenna has worked superbly to routinely reach repeaters 40-50 miles away. The Diamond X30 does not fall off so that I can detect any degradation in signal. (It’s installed to be dedicated as a link radio node.) The Ventenna and Diamond are about 40’ above ground.

My noise floor isn’t terrible, partly because my neighborhood has underground utilities and is on a large lake which omits development in that direction. Battery chargers in my garage have provided the only serious RFI but some ferrite beads reduced those pulses below the noise floor.

I can only speak to my own experiences. But I simply do not see my foil-backed radiator barrier roof material to be much of a noticeable impediment. Good luck with yours!

73,

Frank

I live in Florida in a new home that was built with foil-backed plywood as roofing material. It does wonders for keeping our home cool but I'm thinking not so great for an antenna farm in the attic since our HOA doesn't allow antenna's outdoors.

Has anyone had any experience using an antenna in such an attic? I've read some posts in other forums where people have done it and claim no ill-effects of doing so but common sense is telling me it's not a great idea from both a technical aspect and a safety aspect, especially since the antennas would be right above occupied bedrooms. All the electrical wires for AC outlets, alarm wires and cat5 are also running through the attic since this is a one-story home.

Thoughts? Suggestions?
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WD2AJW

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RE: Attic with foil-backed plywood roofing question
« Reply #2 on: June 28, 2019, 08:46:26 AM »

Thanks, Frank, for your comments. Much appreciated. I am building my own J-pole now for VHF/UHF and intend to try it in the attic first before trying to sneak it outside (which I might do anyway.) It's just easier to keep the coax inside as opposed to trying to run it outside, especially through concrete block walls. Once I get my HF station back together again, I was looking at a rotatable antenna since I do have enough room in certain areas, mainly over the garage. But since I'm a one story home, it'll only be approximately 20 feet off the ground.
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K5LXP

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RE: Attic with foil-backed plywood roofing question
« Reply #3 on: June 28, 2019, 03:37:21 PM »


Something that will reveal just how much attenuation might expect is to use a portable shortwave radio and pick up a station outside (e.g. WWV) then go into the attic and see how much if anything the insulation (or stucco, or whatever) degrades the signal.  Same goes for V/U, using NOAA weather stations at various distances.

Mark K5LXP
Albuquerque, NM
 
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K1VSK

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RE: Attic with foil-backed plywood roofing question
« Reply #4 on: June 28, 2019, 05:11:07 PM »

Another option is to simply remove the foil. Adding more insulation between the rafters would be a more effective insulation for the living space and install ridge vents.

Roofers who I trust have told me the foil increases temperature under the roof shingles thereby reducing the life of the shingles/tiles.
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K4FMH

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RE: Attic with foil-backed plywood roofing question
« Reply #5 on: June 29, 2019, 05:33:59 PM »

Thus is in great dispute. When you contractor built my custom home, I inquired about this and contacted friends at the Dept of Energy where I had received grants to support my work. Roofers May say this but the evidence shows that the average team rise is small and dies not reduce projected viability of the composite shingles. On the other hand, removing the foil and replacing with insulation will act like “an iron,” transferring more heat to the shingles.

https://www.contractortalk.com/f15/radiant-barriers-bad-composition-shingles-327473/

Another option is to simply remove the foil. Adding more insulation between the rafters would be a more effective insulation for the living space and install ridge vents.

Roofers who I trust have told me the foil increases temperature under the roof shingles thereby reducing the life of the shingles/tiles.
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K1VSK

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RE: Attic with foil-backed plywood roofing question
« Reply #6 on: June 29, 2019, 06:05:59 PM »

removing the foil and replacing with insulation will act like “an iron,” transferring more heat to the shingles.


I can’t quantify the heat transfer gain caused by the presence of reflective foil but given it is an excellent conductor as well as a reflector and considering the heat source is above the roof, the conclusion is quite clear.

Regardless, this isn’t worth debating. Removing the foil will greatly enhance the efficacy of any attic antenna with minimal change to temperature in any reasonably well ventilated attic space.
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W8LV

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RE: Attic with foil-backed plywood roofing question
« Reply #7 on: June 30, 2019, 09:48:43 PM »

Horsefeathers.

This was addressed on Ham Nation. Can't recall the episode.
But the foil did NOT cause a significant problem with Ham communications,
in spite of what you are hearing from others here.

You have to be a bit careful here as to who and whom gives you advice, even though it is well intended by K1VSK and others.

I am sure that if you email Bob or Gordo directly,
they will easily recall that. So that would be your best bet.

Bob Heil (K9EID) can be reached at: bob@heilsoind.com

Gordo (WB6NOA) can be reached at: w86noa@arrl.net

They DO answer their mail, and they are GREAT Hams.
And Experts!

73 and All the Best!
DE W8LV BILL


« Last Edit: June 30, 2019, 10:09:50 PM by W8LV »
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W8LV

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RE: Attic with foil-backed plywood roofing question
« Reply #8 on: June 30, 2019, 10:15:50 PM »

Typo Corrections:

Bob Heil K9EID can be reached at bob@heilsound.com

Gordo's address is wb6noa@arrl.net

Sorry about that!

Happy Canada Day, Everyone!

73 DE W8LV BILL
a.k.a. W8LV/VE3

;-)
« Last Edit: June 30, 2019, 10:19:31 PM by W8LV »
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K4FMH

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RE: Attic with foil-backed plywood roofing question
« Reply #9 on: July 01, 2019, 06:06:07 AM »

Hi Bill,

Gordon May have referred to a different ham’s report on HN but I had discussed my results with him just prior to that episode. Gordo did a Skype program for my club that u had arranged. I can only speak for my QTH but others may attribute issues to the intuitive culprit of the foil-backed radiator when its HVAC or other metal objects.

73,

Frank
K4FMH

Horsefeathers.

This was addressed on Ham Nation. Can't recall the episode.
But the foil did NOT cause a significant problem with Ham communications,
in spite of what you are hearing from others here.

You have to be a bit careful here as to who and whom gives you advice, even though it is well intended by K1VSK and others.

I am sure that if you email Bob or Gordo directly,
they will easily recall that. So that would be your best bet.

Bob Heil (K9EID) can be reached at: bob@heilsoind.com

Gordo (WB6NOA) can be reached at: w86noa@arrl.net

They DO answer their mail, and they are GREAT Hams.
And Experts!

73 and All the Best!
DE W8LV BILL



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K1VSK

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RE: Attic with foil-backed plywood roofing question
« Reply #10 on: July 01, 2019, 06:25:50 AM »

Reality check - we should all erect a Faraday Cage made of solid foil around our antennas as there is no effect.


I give up! Common sense and all electromagnetic theory has ‘left the building’ because someone heard than on YouTube.
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W9IQ

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RE: Attic with foil-backed plywood roofing question
« Reply #11 on: July 01, 2019, 07:17:31 AM »

The notion of aluminum foil acting as an HF Faraday cage is not very well founded. The skin depth of HF RF current exceeds that of most common foil cladding or household cooking foil. RF current will therefore flow on both sides of the "cage".

And for the pedantic among us, keep in mind that a single skin depth δ does not contain all of the RF current - it only represents a 63% current gradient. It takes 4δ to contain about 98% of the current.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W1VT

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RE: Attic with foil-backed plywood roofing question
« Reply #12 on: July 01, 2019, 08:13:52 AM »

https://www.floridacondohoalawblog.com/2017/06/25/associations-must-allow-flags/

Florida has a flagpole law that goes into more detail than the national Freedom to Display the American Flag act of 2005.

RF can leak through thin gaps, which is why so many screws are used to assemble quality RF shields constructed out of sheet metal.  Soldering works just fine if you are making a shield out of thin brass or copper sheet, as well as unetched circuit board.

You may wonder how a microwave oven door works as a shield.  
https://patents.google.com/patent/US4137441

« Last Edit: July 01, 2019, 08:19:16 AM by W1VT »
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W8LV

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RE: Attic with foil-backed plywood roofing question
« Reply #13 on: July 01, 2019, 05:20:05 PM »

The Beauty of Ham radio is experimentation and discovery.

You might just want to do a temporary experimental setup of your antenna in the Attic, and see how it goes...  The interactions/reflections of your foil/HVAC/wiring in general, and your individual appliances, walwarts, etc. (And neighbourhoood) may or may NOT cause you problems.

Of Course, there may be some attenuation, as K1VSK says. But it may be insignificant. And highly individual to your QTH. But I'd try that before I started ripping off foil from the insulation, if it were me. Same for UHF/VHF... I'd try the antenna, First. You might be surprised!

Off the cuff, and with no data sheets? My guess is that at HF, less of a problem. And as you move up the scale to 900 MHz? More so. But I can't say how much more so, or less so.

I'm certain that everyone with a cell phone has noticed the Faraday Caging that happens when you get in an elevator and the doors close.

As far as HF recieve, my experience is that on HF SW listening, a lot of the rules don't apply.

My teenage pal Billy Lyons and I had the pleasure of having an old Grundig in his parents basement cave/bar that his Dad brought back from when he was a soldier in Germany. (One of his jobs was to drive Elvis Presley around in a Jeep to his publicity interviews, featuring Elvis in his combat fatigues!)

So anyway, we just ran a wire for our antenna around the ceiling rafters of the basement. And that worked pretty well. We didn't know why at the time, but it worked! Now many years and engineering texts later, I realise that the issue wasn't Signal Strength, it was that we overcame Signal to Noise with that modest setup.

Many an evening of SWL enjoyment was spent there, listening to that Beautiful Grundig  post war blonde wooden set, and Wow the speakers sounded really good. There being a bar located there complete with liquor bottles that his parents always marked on the side with a Sharpie marker so they could "tell" if any was removed, we Of Course thoughtfully used our own "Sharpie" to remark the bottles. And we never got into any Juvenile "Trouble" whatsoever...

So, experiment! You may find that your set works great in Spite of the complely draconian and arbitrary rules imposed by the HOA Jack Boots!

Let us know how it works out!
I'd love to try a QSO with you sometime with your new setup!

I also propose a new Contest/Special Event for those in HOA Occupied Territories to work other ops who are also "living" in other HOAs, all out there making contacts right under the Nose and Belly of the HOA Monster.
The "Nelson Cup" will be an Inspiration for those living in places like North Korea and other HOAs in places like Florida to Get On The Air in Spite of it all!

73 DE W8LV BILL










« Last Edit: July 01, 2019, 05:28:55 PM by W8LV »
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K4FMH

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RE: Attic with foil-backed plywood roofing question
« Reply #14 on: July 04, 2019, 09:47:13 AM »

Hi Glenn,

Indeed! Michael Faraday is a legend...and I built a BCB magnetic loop with an open-ended Faraday Cage to reduce noise back in the 1960s from an article in a MW DXer's newsletter. It's a shame when the "idea" of a Faraday Cage gets to be dogma for the appearance of any large piece of metal, no matter how thing, unbonded, or otherwise porous it might be, LOL!

When we built this house seven years ago, I had no idea that my contractor of this custom home was doing to use foil-backed radiator roofing with a ridge vent. I'm glad he did because of the energy savings. I was shocked when I visited my build site and saw it just after frame-up. But I had my HT with me and was equally shocked that I hit the same repeaters from the attic inside this "Faraday Cage" as I could standing on the street in from of my house. Later, when I had the electricians run my sort-of horizontal loop of #14 THHN wire from Lowes just an inch under the shingle edges, I made a contact with Steve Katz WB2WIK in Malibu CA from central Mississippi on 20M. I then installed an 80/40 dipole from MFJ and other dipoles.

My point is, which underscores your post: empirical observation should most always supercede general, vague suppositions. I don't for a moment think that the foil-back panels (unbonded) help my RF. But it's clear from 7 years of activity that they DO NOT PREVENT me from having a somewhat effective "antenna farm" in the presence of it. My post in response to the OP was one of encouragement, to experiment to see if his site was workable instead of just assuming that the dogma that a foil-backed radiator --- instead of HVAC, wiring and other metal objects --- would degrade or prevent his signals from being effective. I hope others will do this, too.

73,

Frank
K4FMH

The notion of aluminum foil acting as an HF Faraday cage is not very well founded. The skin depth of HF RF current exceeds that of most common foil cladding or household cooking foil. RF current will therefore flow on both sides of the "cage".

And for the pedantic among us, keep in mind that a single skin depth δ does not contain all of the RF current - it only represents a 63% current gradient. It takes 4δ to contain about 98% of the current.

- Glenn W9IQ
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