Hi all, this is my first tutorial so forgive me if it's kind of n00b.
Searching this forum has yielded many awesome ideas for boarding up house windows, but many of them involve either hard mounting wood to your window frame, or use some sort of adhesive Velcro. Having moved into a new home, I needed a clean solution, no holes, no residue. So I have made my boards to mount magnetically to my window frames.
STEP 1 - Secure some magnets:
The type of magnet I use isn't the store bought kind. The run of the mill black magnets do not have enough hold power. Instead I use Neodymium magnets. These are rare earth magnets that I harvested from defunct hard drives. There's a ton of info that you can Google on harvesting these magnets so I won't go into of those details here. I'll just say that these magnets are incredibly strong, and free if you have access to old computer hardware, or have some old hard drive sitting around doing nothing. Recycling is good!
Step 2 - Measure the Windows:
Easy and straight forward. Make sure you get all the dimensions, length, width, depth of the frame and also point of attachment. For my needs, I needed to build a frame that was 57" high, 33" wide and attachment point 29 inches up from the bottom of the window frame. I also needed a depth of 3" so that when I mount the horizontal slats, they would actually overlap the window frame instead of sitting inside of them.
Step 3 - Gathering Materials:
Here is what is needed:
- A good supply of 1x2's, I got mine at Home Depot, cost about $1.50 each. The amount needed will depend on the dimensions of your windows. For I only needed a single 1x2 per window.
- Screws, I used deck screws for my build.
- Duct Tape, never leave home without it.
- Paint, mainly black, but also a lighter gray, make sure it's latex acrylic. Other paints may dissolve the EPS foam.
- EPS foam board. This will be used to make the actual boards for the window.
- Velcro (optional if you want a non-permanent build, get into that later)
- Glue, I use well bond, it's awesome stuff.
- Sand Paper, medium grit for sculpting he foam.
STEP 4 - Making the frames:
So to keep the frames lightweight and easily storable, these frames are 'H' shaped. I did this mainly because my attachment point is mid window. I marked and cut two 57" pieces and a single 33" piece from each 1x2.
Because I needed a 3" depth, the horizontal 33" piece is laid flat, and the 2 57" pieces are attached on edge with one screw. I also used the scrap end of the 1x2 and screwed it into the center of the 'H' as another spacer to give the frame a little bit more depth. Use the duct tape to wrap around the horizontal piece to reinforce the 1x2 as it may start to crack a little when putting the screw in.
Assemble as many as you need.
STEP 5 - Making the Slats:
*SAFETY NOTE - WEAR A MASK WHEN SANDING EPS FOAM, IT'S NOT GOOD FOR YOUR LUNGS*
Using a sharp utility knife, I cut the EPS foam board into 2x36" pieces. Again the length will vary depending on the size of your windows. I figured I needed 4-6 slats per window to achieve the look I wanted.
Using the sand paper, I then sanded details into the foam. I cut out a 3x3 square and fold it in half. Using this edge I can then carve out wood detail, adding chips, splinters, etc to the foam. I also go over the whole piece with a light sanding to give it a roughness. It also helps the paint to stick better.
Make as many boards as you need.
STEP 6 - Paint:
Using the black paint, paint all the 'H' frames and EPS slats. It may not be necessary to paint the back of the 'H' frames as they will be out of view. For the slats, make sure you get paint into every nook and cranny. Some of the deeper detail might get missed and you will have pink spots after the paint has dried. Allow at least 24 hrs of dry time before the the next step.

STEP 7 - Dry Brushing:
Now we are going to add detail using the gray paint. Lightly dip the tip of the brush into the paint, getting very little on it. Then using the paint can opening, brush off even more paint from the brush. The idea is to have as little paint on it as possible.
I start with a single stroke across the top of my boards first to get the wet edge off of the brush. No one will really see the edges so it doesn't have to be perfect. Then I use random sweeping patterns, in all directions until I achieve the look I want. It may take more than one pass. Take your time in doing this, otherwise you may end up with brighter areas of paint that are hard to cover up. Make sure you get the left and right edges too as they will be visible.

STEP 8 - Putting it all together:
First thing to do when the 'H' frames are dry is to attach the Neodymium magnets to the horizontal brace. I used painter's tape as I don't want a permanent attachment. Simply wrap the tape around the magnet and frame a few times. Just make sure that you don't overdo it, as this weakens the magnet a little bit.
I used Velcro as I didn't want my slats to be permanently affixed to the 'H' frame for storage reasons. If that's not a problem for you, glue them into place.
Finally stick the sucker onto the window frame making sure that the 'H' frame sits on the bottom of the window sill. The picture below is the assembled prop stuck to my garage door.
Here are a few on the house, the rest of the windows will be done as well.

There you have it, a good secure way of doing boarded up windows without having to drill, nail or adhere anything to the house. Thanks!
*UPDATE*
So far so good, survived 1 light snowstorm, 1 heavy, wet snowstorm, and a few high gusting wind situations. Wind is blowing 30-40 km/hr right now and the boards don't budge. The webbing I put up however looks like poo. Gotta redo them before the big night.