PowerShell v2+, 99 90 bytes

param($n)1..$n|%{" "*($n-$_)+"/----/"+-join(" "*($n+$i++)+"\    \")[($n+6-$_)..($n+5+$i)]}

To that, we add another string that's been sliced [...] and -joined back together. The second string is the slide, and we assume that the whole slide is always visible. It's the number of spaces before the slide would start " "*($n+$i++), followed by the slide itself "\ \". This is sliced by a range calculated out to be the part of the "spaces plus slide" that's partially hidden by the ladder.

PowerShell v2+, 99 90 82 bytes

param($n)1..$n|%{" "*($n-$_)+"/----/"+-join(" "*($_+$i++)+"\    \")[6..(6+$_+$i)]}

To that, we add another string that's been sliced [...] and -joined back together. The second string is the slide, and we assume that the whole slide is always visible. It's the number of spaces before the slide would start " "*($_+$i++), followed by the slide itself "\ \". This is sliced by a range calculated out to be the part of the "spaces plus slide" that's partially hidden by the ladder.

PowerShell v2+, 99 bytes

param($n)1..$n|%{$x=" "*($_*2-2)+"\";if($_-ge4){$x=" "*($_-3+$i++)+"\    \"}" "*($n-$_)+"/----/$x"}

Takes input $n, starts a loop from 1 to $n with |%{...}. Each iteration, we set a helper variable $x equal to a number of spaces and a \. This is calculated out to be the top part of the slide that's partially hidden by the ladder. However, if we're at (counting from the top down) rung 4 or greater, we immediately change our mind and set $x equal to enough spaces $_-3+$i++ and then the full slide width \ \. Next, we count out how many prepending spaces we need (based on how tall our slide is and where we're at $n-$_), followed by the ladder "/----/ and our previous variable $x".

PowerShell v2+, 99 90 bytes

param($n)1..$n|%{" "*($n-$_)+"/----/"+-join(" "*($n+$i++)+"\    \")[($n+6-$_)..($n+5+$i)]}

Takes input $n, starts a loop from 1 to $n with |%{...}. Each iteration, we're constructing a string. We start with the appropriate number of spaces " "*($n-$_) and the ladder "/----/".

To that, we add another string that's been sliced [...] and -joined back together. The second string is the slide, and we assume that the whole slide is always visible. It's the number of spaces before the slide would start " "*($n+$i++), followed by the slide itself "\ \". This is sliced by a range calculated out to be the part of the "spaces plus slide" that's partially hidden by the ladder.