First of all the center of single story wood frame house gives you a 50% reduction in exposure. (I believe this assumes your windows and doors are closed and radioactive particles are not blowing inside.) This report makes an observation that I never seen before. There is more exposure from the ground outside the house than from the roof. (p. 17) Those of us with a significant slope behind the house should probably bias Shelter Cramer towards the slope side of the house. My suggestion awhile back about building a box of ammunition in which to take refuge may need some modification. (I am sure most of my readers have 10,000 rounds of lead shielding combined with brass in little boxes.)
It would appear that building a wall around you might be a more effective shield than a ceiling of lead. Two inches of lead gives a reduction of about 1/8th. Let's see: two boxes of .223 stacked with ammo facing outward should give us something approaching 2" (and the brass helps also, as does the metal of the ammo cans.). Put all this under your kitchen table near the center of the house. Combined with the 50% reduction of your house this means about 1/16th reduction. Now stack all your bottles of water and canned food inside the lead wall, or on top of the table where you can reach it with minimal exposure. Water is not a great shield (low density) but at least irradiated water produces very little secondary radiation, unlike heavy metals. Maybe all combined you get a 1/20th reduction. You also want food and water where you can easily access it. You are probably going to make hopefully short visits to whatever bathroom is most interior to the house. Water may not continue pumping unless you have 1000 gallon gravity fed water tank like my last house, but even failing to flush will be less stinky and unpleasant than using a 5 gallon drum as a toilet. A proper fallout shelter is a reduction to 1/40th, so for a improvised shelter, this is not too bad. This is not ideal, but if you are over 50, the postwar chaos, starvation, and cannibalism (aren't I cheery today) are more likely to kill you than cancer.
UPDATE: As I was thinking about this, it struck me that having your ammunition wall bunker near the kitchen or laundry room can be advantageous: a refrigerator, stove, or oven all have a fair amount of steel which will certainly contribute to attenuation. If you have marble countertops or the artificial kind (Silestone) these are not much inferior if at all inferior to concrete for shielding. Put your under table shelter in the shadow of these so that fallout on neighboring roofs and trees had to go through these as well.
Of course the best improvised shelter if you have enough warning is dig a six foot deep (that deep so you have room to move around, and if it does not work, you simplify the work of whoever buries you) and long trench, put doors on it and pile dirt three feet deep. (Earth arching effect will distribute the load to the surrounding ground, preventing collapse.) Next park your cars on top to add another layer of metal shielding. Remember you need an entrance after the cars are parked. The simple solution is to drive them across the trench to get shielding from the ends of the car, but I would worry the weight of the car might be too much load for earth-arching. Drive them on top longitudinally and stay near the engine block ends of the trench.
You still want those mountains of ammunition between you and the entrance.
Not enough ammo? AmmoToGo has an ad on the right side.
Because Putin has been making sort of under his breath reminders that cutting them financially does not preclude them from a nuclear Gotterdamerung, I have thinking through bolt out of the blue scenarios (yes, I am having trouble sleeping). There are only two nearby targets: Boise (state capital) and Mountain Home Air Force Base. These are 28 and 68 miles away, respectively. A detonation at either location would generate a flash that should wake even the heaviest of sleepers. That is instantaneous for practical purposes. At that distance prompt radiation is completely absorbed. The blast wave is 2.8 or 6.8 minutes later. With a little care you can open all the windows in your house so the shock wave does not break the windows. (As near as I can compute even a one megaton bomb will not break windows that far way) This not only reduces risk of glass cuts as you madly build your fallout shelter, but also lets you close the windows before fallout blows in from Portland, Seattle, Bremerton, and Hanford. It is probably wise to calculate blast wave arrival time from your nearest targets. Blast waves move at roughly the speed of sound (300 m/s).
