Building in GURPS

Building in GURPS

As you all know, in order to be a man, one has to plant a tree, build a house, and father a son. GURPS doesn’t seem to have rules for fathering sons or planting trees, but it does have rules for building houses. And why stop at building a house, when you can build a wall around it, then turn your house into a keep, and then add a barbican and guard towers? This topic yet again is inspired by ACKS II domain management rules that require a domain ruler to have a stronghold of a sufficient cost to be respected by those who live in his domain.

The rules for construction can be found in GURPS Low-Tech Companion 3: Daily Life and Economics. They are similar to rules for crafting, and why wouldn’t they be? After all, you’re crafting a building. And just like the crafting rules, the construction rules may seem complicated, but they really are not. Let’s go through the process step by step.

Step #1: Calculate building statistics

Buildings have such statistics as HP, HT, DR, Cost, and Weight. All of them depend on the building’s size, material, and thickness of walls. For a simple wall, you just multiply length by height in feet, then multiply by the cost and weight of the appropriate material, and then, if your wall is thicker than 1 inch, multiply by its thickness in inches. Wood is a special case because its cost varies with thickness, because thin planks are harder to make.

Proper buildings are a little bit more difficult to calculate. First, you find the volume in cubic feet. For a rectangular building, it’s as easy as multiplying all of its dimensions, but other shapes need different formulas, possibly with approximation of some degree. Then, you multiply this volume by average wall thickness in inches, and then by the partition factor. Partition factor defines how much space is taken up by internal walls. If this is just a box without any internal walls, then the partition factor is about 0.25. For stone buildings, it’s unlikely to go above 0.42, but thin wood walls may result in a partition factor of 1.25. This is one of the parameters that may require some approximation and guesswork. And only then you multiply the resulting modified volume by the cost and weight of the material from the table.

Step #2: Apply modifiers

In Step #1, we got the base statistics, but they can be modified with certain options, just like regular equipment. For example, there are construction quality modifiers for unskilled or masterful labor, cheap or fine materials, etc. For stone and brick buildings, statistics may change depending on TL because mortar affected the quality.

Step #3: Calculate construction time

Now that you’ve got the final stats of the building, you can calculate the time it takes to build it. As always, the cost is split between material cost and labor cost. The percentage of labor cost depends on the material of the building and can range from 1% for ashlar to 30% for thatch. You also need the monthly salary of a builder – a mason for stone buildings, a carpenter for wooden buildings, etc. For example, a mason has a salary of $900 per month. This salary is multiplied by 0.55 to find the average labor rate, because construction usually involves only a small number of skilled craftsmen and a large number of helpers. Then, if you need to produce the materials, you divide the full cost of the building by this average labor rate to get construction time in man-months. If you have all the materials at hand, you multiply the cost by the labor cost percentage first. That’s it.

Let’s have some examples.

Example #1: Stone Wall (100’ long, 30’ high, 5’ thick)

Let’s make a stone wall that is 100’ long, 30’ high, and 5’ thick. I have to remind you that thickness should be measured in inches, so we should convert it to 60 inches. Multiplying 100 x 30, we get 3000. Rubble costs $3.82 and weighs 14 pounds per inch of thickness. Thus, we get weight equal to 3000 x 60 x 14 = 2,520,000 lbs. or 1,260 tons and cost equal to 3000 x 60 x 3.82 = $687,600, It has HT 12 and DR equal to 12 x 60 = 720. Its HP value is 100 x cube root (1260) = 1,080. Let’s not apply any modifiers.

                As for construction time, construction labor cost is 5% of the calculated cost for rubble constructions. A mason’s monthly salary is $900, and the average labor rate is $900 x 0.55 = $495/month. Thus, if we need to dig up the rock to turn it into a wall, it will take us $687,600/495 = 1389 man-months. A hundred of workers would be able to do it in about 14 months. If the site is full of rubble that can be used for construction, then the construction time is $687,600 x 0.05 / 495 = 69.45 man-months. Thus, a hundred of workers would be able to do it in about 21 days.

Example #2: Wood Cottage (30’ long, 30’ wide, 20’ high)

Now, let’s build a wooden cottage for a peasant. The building will be 30’ feet long, 30’ wide, and 20’ high. I decided to go with the cheapest options here, because this is a peasant’s home after all. Walls are going to be 8 inches thick, because this yields the lowest cost. I also apply the unskilled labor and cheap materials options that decrease cost, DR, and HP. For the partition factor, I chose 0.3, because this small of a cottage is unlikely to have many internal walls. Such a building costs about $32k, and can be constructed in 15 months by a single person from materials that are readily available. Chopping trees and making planks would multiply the construction time by 5.

Example #3: Medium Round Stone Tower (20’ diameter, 40’ high)

Now, let’s build a round stone tower, just to change the area formula. The walls are going to be 5 feet thick. I will add the embossing option that will increase the cost slightly, but add DR against crushing damage. The book seems to imply that the partition factor should be 0.25 here. We end up with a cost of about $791k.

Now, why did I choose these specific examples? These are some of the structures from ACKS II, and I wanted to compare the costs, since I already mentioned that it seems that 1 gp in ACKS is roughly equal to $100 in GURPS. The wall costs 7,500 gp in ACKS, which should be about $750,000 in GURPS, and our cost was $687,600. That’s close enough.

                The cottage costs 300 gp in ACKS, which should be about $30,000 in GURPS, and our cottage costs $32,659. This is very close.

                The tower costs 22,500 gp in ACKS, which should be about $2,250,000 in GURPS, and our tower costs $791,656. This is not close at all! Interesting. Perhaps, there are different assumptions that I’m missing, or the costs were derived in different ways. To get the ACKS cost, I’d have to increase the partition factor to 0.7, which seems too much to me.

                But anyway, that’s how building stuff works in GURPS! I hope that was informative.